The 30 yard and 50 feet targets were custom designed to align the scores with Minutes Of Angle (MOA). The idea behind them was that you could correlate your score to the MOA your shots remain within.
From the top line of the 50 feet target:
" Score(MOA): X(<0.5); 10(<1.5) 9(<3) 8(<4.5) ...1(<15)"
means that if you score all "X", you just shot one heck of a group with all shots inside half an MOA. All shots scoring 10 is a 1.5 MOA group, all shots scoring 9 is a 3 MOA group, etc. The targets go out to the 10 ring, which is a 15 MOA group. Hence the file names start with MOA15...
The 30 yard target is almost the same, except if you shoot all "X" you just shot a 0.75 MOA group - still spectacular. And the 30 yard targets only go out to the 7 ring. Shots scoring all 7's or less are a 6 MOA group, so the file names begin with MOA6.
You'll notice that ignoring the X's, both targets score the same in terms of MOA. Hopefully shooters will find that their average score per shot on both targets is about the same, ignoring more potential for wind drift at 30 yards than at 50 feet.