Just got back from the range.
Feed/Function/Extraction remains 100%.
Heavy-Long trigger remains unchanged.
Initial firing resulted in exact same low-left pattern I've always had.
But after changing grip, trying different finger placement, and making sure I had a VERY FIRM/Tight Grip, it started grouping better.
Looks like the sight-hold, trigger finger placement was NOT a major cause.
I'm guessing a high velocity round in a short gun recoils with more force than I was used to, and it helped to "death grip" the shorty thru the firing cycle....especially important with a heavy/long DA.
My 9mm Shield 2.0/Apex seems to handle recoil better, along with the Hogue Rubber grip sleeve I have on it.
More range time is obviously needed and I have some 115 grn Blazer Brass 9mm inbound, which is what HK used for the test firing.