Since you mentioned thinking about going back to a Ladder Test - this might be interesting to you.

I don't personally subscribe to either philosophy by the letter, and I honestly consider comparing both methods to be one of those "distinction without a difference" type practices. They really do the same thing, just with a different target shape.

I was bored this evening, so I converted your OCW target to a ladder test by placing dots over all of the bullet holes, then superimposing them all onto one target as if they were all fired at the same POA, then assessed for elevation changes with changing powder charge. I placed a box around each group to determine where the center elevation for each would be, then placed its respective coloured line and indicating number.



So in this picture, you get the same result: There's a lot of elevation change bouncing back and forth between 1, 2, 3, and 4 as you raise the charge weight, then things seem to hold pretty stable between 4, 5, 6, and 7, with a big jump in elevation again between 7 and 8. So just like in the OCW assessment, shooting this as a Ladder Test would have shown the same preference for dropping somewhere between 5 & 6.