I generally don't see shot drop at turkey ranges(under 50 yds.) What you will see is the pattern opening up and sometimes some holes developing. I start with my 40yd pattern and when I am satisfied I check my center of sight at twenty or under just to be certain . At close range using turkey chokes you don't have much room for error . You want to make sure if you get a close shot you won't be off to one side or high /low. Other than that , I've never found I had to compensate for any kind of pellet drop at reasonable ranges . If your pellets are maintaining lethal energy (velocity) at forty yds or even fifty, they won't be dropping yet . If you find yourself seeing patterns dropping you are probably exceeding the lethal range of the loads you are using.
At 40 yards with a load traveling 1200fps, you will see about 2 inches of drop from a perfectly level barrel. The load should reach its target in just over 1/10th of a second.
Pellets begin dropping immediately upon being fired, regardless of density or velocity, so there is some validity to your question, just not enough to warrant holding high at turkey ranges.
Yesterday did some target shooting with my 20. I started with light loads at 20 yds. until the pellets were centered on the POI. I mover to 40 yds. and shot my HTL 6's and found the center of the group had moved to approximately 3" high.