What do you see when you dry fire the two pistols with a laser or MantisX or some other comparison — same issue? Aimed slow fire same as “urgent”?
If you haven’t shot for a year, then “more used to” might be a weak rationale, unless the larger gun is more challenging for your hands to grapple with.
Glock G43 vs G17 Gen4 size comparison
You mention that your 17 is relatively new (absolutely new?) while the 43 has been with you for a while. I shoot M&P9, but I shoot my 3.6" compact noticeably better than my partner’s 4.25" full size. I didn’t notice a particular difference when sighting both guns new, but since then the 9c has had thousands more rounds through it and the trigger has become much smoother (and more familiar). Better trigger is my theory for why I perform better with an inch less sight radius, at least until I get past 15yd. The grips on the two M&Ps are only different in length, not reach or circumference.
Only you can say if a couple inches farther away is making your front sight harder to see. It will muddle your stance a bit, but you might try pulling the 17 in a couple inches and see if that tells you anything about focus.
Like everybody else says, it could also be technique — but don’t rule out the guns as a possible factor. FWIW, I can’t shoot off a rest worth a darn.