I know of a great park where elk appear before dark. Like many such places the convexity of the open area makes it unlikely to see elk when on the ground there. I found a cliff vantage point that would offer shots from 250 to about 600 yards. The downslope is 21 to 26 degrees. For me, the easiest method is to just apply the cosign rule. My question is whether you have found it reliable enough for steep shots at fairly long ranges. It is surprisingly hard to find a place to test this out.