Range to the target ( straight line, regardless of angle whether up or down) then measure the angle from shooter to target, look up the cosine if the angle on your data card- you probably can skip all the details and do every 5 degrees- maybe to 50 0r 60 degrees if you think you’ll ever shoot that steeply then simply multiply the gun-target line range in yards by that decimal ( it will be less than 1 from zero to 90 degrees), and shoot for that number.
Example- if your range is 9oo, and your angle cosine is .9, your actual range to the target is 810 yards. Hold over or dial in 810 and shoot. f the GT range is 400, the cosine is .80, then the actual range is 320.
In effect, the real issue is horizontal range, not shooter to target line distance. All the rest is noise.
This explains how to compensate, which was not the issue.
The issue is what are the physics which account for the counter-intuitive result — point of impact is higher (and effectively equal for the same up/down angle).
Flight time doesn’t change. Distance to target doesn’t change. Drop doesn’t change (the effect of gravity is still the same).
Explaining this is where shooters come up with the amusing and the absurd.