Follow up: I am dumb.
I was in a rush to get to the range and home again with the G19X the first time I went that I didn't realize I didn't put my normal medium backstrap on. I think that was the issue with my shooting mechanics that day, not the sights.
I was under that working hypothesis when I laser checked the bore and found that the sights were pretty spot on.
It does seem more like a combat sight picture rather than a half-and-half, but still was easily hitting 8" steel at 50 feet in the limited shooting I was able to do this weekend. So FWIW, it does seem like the 6.1 is a reasonable Gen 5 rear sight.
Also FYI for people, Sig Sauer uses that sight picture on their firearms.
Off the Sig website:
https://www.sigsauer.com/support/faqs/
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My SIG SAUER pistol is not accurate. Why? What should I do?
All SIG SAUER production duty/combat pistols are set up to use a “combat” sight picture. This is where the
front sight completely covers the bullseye of the target. Using a six o’clock (“pumpkin on a post”) or center mass (“half’n’half”) sight picture will result in low impact. SIG SAUER, Inc sights in all non-sporting and non-target pistols for 2.5 inch groupings @ 15 yards. If you are still having trouble please contact Customer Service for further help and instruction. Please have your serial number ready. There are also very helpful free Internet sites that cover pistol group analysis.
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