New pin design and an alloy change yielded promising results.
The new pin is smaller in diameter and set deeper with a long taper and only radiused at the bottom of the cavity with a step at the crimp groove. I changed the alloy to a straight 15-1 (with whatever trace antimony hides in stick-ons), and drove these at about 1100fps into wet-packs. Both penetrated to 5 1/2 to just shy of 6", retained much of their nose portion, and expanded very well. I think my 2-legged varmint boolit is just about dialed in.
Just FYI, the pin "looks" off-center because I had to hold it open on-angle to get it in the photo. It IS centered, just tipped back to see the cavity without the other half of the block getting in the way.
For comparative, here's the original pin design and depth setting.
