View attachment 53654
This mishmash would be lessened if the holes at the 4 corners were relocated. This is done by sizing the seat differently.

Now have a look at the seat below. No mishmash at the edges - that's because while the majority of the holes are spaced at 20mm apart, the holes at each corner 15mm apart from the two nearest holes (ideally they should be 10mm apart, but this causes problems due to the thickness of the cane).

Well I'd never even thought about that, but worse, I'll probably forget by the time I make my next seat.