There's a thousand variables in play, and many of them are on the shooter. There could be some difference between one person and another. But from my experience, it's usually pretty close.

If they're grouping them tight, then move the sights to work with them is my philosophy. And there's calculators for the uphill/downhill shots. I have a laser rangefinder with a built in angle calculator that gives you the number in horizontal distance instead of line of sight. Ballistically, that's supposed to be the number that matters. When hunting, I've got a good idea of exactly the right number for my possible shots from that stand.