I would think that with rifle velocities that no compensation at all would be needed at all at thirty yards.

The easiest way to verify this is to get the laser range finder from Opti-logic for archery which measures the actual vertical angle down or up and gives you a corrected horizontal distance to shoot.

I have ordered a laser range finder for rifles out to 1000yds to compensate for the various angles uo and down when shooting in the mountains.Be aware that serious adjustments in holdover are needed at distance when hunting steep angles in the mountains.That 350 yd upward shot may actually just shoot horizontally like 275.

Does it matter?? At signifigant distance you betcha!! At 30 yards my gut says It comes down to shooting technique and shouldering the rifle at speed at a different shooting angle than horizontal but that can be verified easily.