I think this is why it is deemed irrelevant. . .If you are 20 feet in a tree and the deer is ranged at 20 yards, the angle is 18 degrees. That makes the corrected range 19 yards. Sure you will say but at 40 yards?? 39.5 yards is the corrected range. Uh at 10 yards or 5 yards the numbers are much more extreme, but with a TBR of 1 - 10, that is the same point of aim for me. At longer rifle ranges, unless you are shooting off a steep hill > 600 yards, it is unneeded. 600 yards, 30 deg hill = 543 yards. Now this is where it starts to matter, but even there, you can get close by saying: 0 = 0,10deg = .98, 20deg = .95, 30deg= .85, 45deg = .7. You can be even more exact with a protractor with a string and a bolt attached, or some other cheap and easy inclinometer. I prefer to guess since I realize most of the time slope = 10deg or less. more extreme slopes might be 20 - 30deg. If I were a ram or sheep hunter, I might rethink.

Also, the inclinometer rangefinders have a rep for not being able to range well, for orther quality reasons.

Besides, even with a rangefinder bowhunting, I only use it to setup. When shooting, I just estimate based on the trees I ranged while setting up.