When I was having a go at at 100M shots some time back the pellet was just disappearing into the grass somewhere well before the target, I pinned the target to the top of 6 feet of plank to see the actual drop to I had to compensate for, I think it was about 20". As a footnote, the plank was 8" wide & the slightest bit of breeze took the pellet past it.
I used 20mm circular black stickers, from 'Shoot & C' - they go DayGlo yellow round a hit? To be honest there wasn't much yellow in evidence but it was fun trying...