I particularly like the fly, P.F. nice one.
I would be interested to see some landscape/buildings, and see how consistent across the frame yours is. My f2 close focus, PKA mount, fairly worn example, isn't (the kiron made ones I have do a bit better)!
My investigations indicate that the main reason is
field curvature. When I move the 10x magnified image in live view from the centre to the edge (you can use the 4 way controller to do this on K3 and other models), I can improve the focus by slightly refocussing (nearer).