I'm not doing a great job am I?
I'm suggesting that the pellets that have the 40fps difference at 55 yards may be pretty much the same as the others right up to becoming unstable right at the very end ... so the poi's remain almost the same ... ie same vertical ... like we are seeing.
We are judging as if they started with 40fps difference and then travelled the whole 55 yards.
2 almost identical cars race over 1/4 mile and are doing the same speed and are neck and neck with just yards to go. One car slams the brakes on near to the end and crosses the line in second place just behind the other car. The speeds are measured as they both cross the line. The second car has a speed 30mph slower but he's only been going 30mph slower over the very last part of the race so he only loses by a short amount ( total times almost the same = poi almost the same = still same vertical ).
You can't say that the slower car's finishing speed was 30mph slower than the winning car so it should have lost by a lot more ( as if it's been 30mph slower for the whole 1/4 mile ).
So the pellet groups will be excellent at say 45 to 50 yards ( say only lost @ 25fps at this point ... and we know pellets that have 20 fps spread at the muzzle can give great groups at 55 yards ) and then one pellet starts to break down ( unstable ) but still holds pretty much the same vertical at 55 but is now doing 40fps less ( so lost another 20fps at this late stage ). If it were tested at 60 yards the poi would be much lower. Can ballistics not work like that?
Just frying my own brain ... sorry.