if you hunt big game with a rifle and shoot inside 350 yrds there is no need for the actual horizontal, maybe in angles greater than 40 degrees. BUt a flat caliber rifle will eliminate your mistake (MPBR). Or if you bow hunt where knowing the distance is crucial, steep angles do come into play...
I shoot sheep at angles, but have learned to subtract some distance when shooting up or down at steep angles.rest of the time wind is the bigger factor.. dont worry about the rest, its just overcomplicating a shot. IMHO
