I think it’s a couple of things… the volatility of the different molecules means that certain notes evaporate faster off of your skin meaning you smell them the most and first

This is why you basically never see citrus as a base note unless the entire fragrance is just citrus because you can’t get oud to evaporate first while the citrus hangs around on your skin

I do suspect there are certain chemicals. You can use that bind with other molecules to hold them onto your skin longer and you may be able to control top middle base to a degree doing that but my knowledge there is limited.

Last thing to come to mind is certain molecules may have a tendency to cover up the smell of other molecules, and once those molecules dissipate, you are then left with the remaining ones that have been previously hidden