Put your target out and shoot at 20 and 30 and measure the difference, mine was about 5" difference from what I remember with my DXT at 70lbs shooting maxima red SD's. I hunted many years with my top pin split from 20/30. I think with elk it won't be enough to matter if your to pin is dead on at 25 or 27, etc. you will be good from 0 to 30
In regards to your question above, I'll back up if I'm closer than 20yds and get dead on 20 to make a better shot on a grouse. Deer and elk, I rarely consider an adjustment under 20, maybe on a deer aim a little more for heart i f I have time to think about it.
Try 20/30/40, 25/35/45, and 30/40/50 and see what feels better.