This is a fairly complex issue and has a lot of nuance.
Hot and cold cup:
There are aromatic compounds and flavor compounds. Some may be soluble in water and others may be insoluble, so you can smell them in the dry grounds but not taste them in the cup. Because some of the flavors are not able to be dissolved by water. Also, the molecules’ weight and the water temp also change how all the molecules acts. Heavier molecules do not evaporate as easy as lighter molecules and so you do not smell them because they could be left in the cup or are oil soluble and are not easily released. Or it is possible that there are more of molecules of one flavor blocking your ability to smell the less available (although more desirable flavor) as so one must wait for those less desirable but more of that odor to evaporate away or re-condense as the cup cools.
I do not know how to do this by changing the roast yet and why some of the African’s don’t smell like much hot, but as they cool down the aroma and flavor changes and I can taste them. I agree that a great roast is front to back, hot to cold full of those great flavors (caramels, fruits, chocolate, whatever it is as long as it is clear and distinct). I have roasted the same bean where I got great flavors on the hot cup and cold cup and other roast profiles (same bean) only on the cold. And so, I believe that it is achievable by roasting, but precise roast techniques and gypsy magic are still unknown to me. What I would guess is that the quick oxidation as the cup is cooling creates these odors (or could just be there already from the roast but not in such a high quantity to smell/taste it hot and cold). But odor molecules of the hot cup can be different than those of the cool cup and each (can taste the same) are dependent on the roast and rest, formation of these flavors and aromas.
Fresh vs rest:
The premise that a darker roast needs more rest time. But letting a lighter roast rest can also develop nice flavors different from immediately roasting and drinking.
If I’m grinding under a couple days rest (on the side of a “fresher” coffee) those tastes, and aromas are based solely on the heating of the roast with little time for the flavors made to mature together into something different. If I am not roasting deep or hot enough to create lots of the pyrolysis reactions (and in later part of the roast; breaking down of the cell wall causing pathways for the oils on the inside of the bean to move outside) and thus CO2 and gas products which need resting time to form the flavors. It is possibly because the oils are not on the surface and have less exposure to oxygen and thus change the flavors tasted. Those later pyrolysis-based reactions result from the formation of what I assume are the called beta-oxidation reactions which happen after lots of rest, when the oil interacts with the broken down cell walls, maybe starting 10 to 14+ days rest for Arabica and 30-45+ days for Robusta in a non-oxygen rich container.
The flavors and aromas created can vary in weight and structure but smell similar. Meaning if I roast lighter and don’t break down things as much, I might still achieve a flavor found in a more heavily roasted coffee. I don’t know if any of this is 100% true for what’s going on, but the guesses are based on science and anecdotal evidence. I.e. why a Mexican bean can taste chocolaty lighter, but Brazilians of Africans need heavy/deeper roasting to taste chocolatey.
When it comes to extracting, the concentration matters. Other molecules that buffer or block the ability to taste/smell them and so concentrating OR diluting the extract (espresso, etc) helps express some of the aromatics or flavors. Again, whether it is appropriate to provide enough water to extract everything. Or concentrate the flavors in less water, ristretto vs lungo, gives the flavors and aromas the ability to be perceived via smell and/or taste.
In the dry aroma: In the whole vs ground
This can also be determined both on roast and rest. The molecules created from the degradation via heat used condense and break down fluids in the beans or be taken further to breaking down of the bean cell wall structure and causes a change of flavor during the rest period, changes in the chemical aspect occur because of molecules made available during roasting and then flavors “maturing” or forming during the rest period.
Some determined factors may be the amount and quality of “juice” in the bean to begin with, the size of the pores and how far into the roasting the beans went. When the pores or individual cell walls expand by heat breaking down and weakening the cellulosic/cellular structure that is the bean structure. The cell structure breakdown occurs in the greatest degree during second crack (aka secondary pyrolysis crack) but the path the roast takes has an impact on its formation, not just the crack itself but the overall degradation of the bean structure. And how heat applied from beginning to end builds up to the Second Crack phase, the breaking down of cellulose (and other bean structural: hemicellulose, ligin, etc components without burning) causing micro cracks. Allowing the oil that was formed/dehydrated and condensed within the pores of the bean to escape by being pushed out from heat and pressure, the oil through the micro cracks to the surface. Making the flavors aromas more available to be formed seen and smelled will be slowly oxidized (maybe "oxidized is the wrong word) during rest to form new flavorings.
Since the breaking down of cellulose also changes the flavor profile. And navigating the end results is based on the roasters (person/profile) ability and material used. I think the best ways to illustrate this is to look at a good Lapsong Souchong tea. After a year to a couple years the tea comes into wonderful fruity and spicy aromas and taste. This tea is originally black tea roasted over an aromatic wood and thus smoked. In the beginning if you tried the tea it would taste just like smoke but resting and an oxygen free environment over a long period of time the tea really changes and matures in taste. I only bring this up because I’m on a break from coffee and have switched over to tea. And it is on the tip of my tongue. When you open a new bottle of whiskey and pour out small portions over a long period of time 6-8months there are more flavors. Same with wine and pouring a half glass a day, recork the wine and leave it on your counter and every day you drink the wine you’ll see the wine “open up” because of slow oxidation that is occurring.
And so if you roast to a medium roast those oils aren’t created on the beans surface (and don’t have a way to move out towards the surface of the bean).** When you grind the bean you are exposing the open pores/pockets and those aromatic smells (oil droplets, formed on the inside of the pore during roasting) and the release of the gases are now able to evaporate/escape and so you can now smell them. Whether or not they are then able to be dissolved in water, or in large enough quantity to remain so you can taste them is another story and dependent on that specific molecule and quality of the roast.
**I have had multiple Africans that didn’t oil, but literally right after roasting, literally, there was full on strawberry smell that lasted for 3 days. No exaggeration, no lie. And that was using the African profile for wet processed “MELFS 3.4(v.2)”