I suggest you shot paper a200, 300, 400 from that higher vantage point and you can see where it shoots.

Try this . . . whatever your balistics are, zero that much high at 100 yards so you would be zero at 200. For instance, .300 win mag in 180 gr nosler zeroed at 200 is 1.5" high at 100. Then shoot from up the hill at 200 and see if it's still dead on or not. I think you will find that it is shooting a fraction high because you need to aim low whether shooting uphill or downhill. Capice? How much off it is will tell you if there is a drop differential.