I thought I would separate this from Hammer’s thread.
I started to get frustrated with finding new shoes, so opted to try a custom fit. The fitting process was interesting and eye opening. One foot was as much as 13mm bigger in girth, which was measured in four places.
This might explain two things I had noticed in the last 18 months. I always have to tighten the strap on the smaller foot a click or two after a few steps, not tragic. The bigger foot has been prone to noticeable pain around some joints after a long time on the bike.
Maybe the difference amounts to half a size, so one shoe is never a perfect fit. Maybe I’m just getting old enough that my body doesn’t get over discomfort as easily, or I just need something to complain about.
I’ll find out if a perfect fit is possible in about a month, give or take pandemic border crossings, and report back.
I have the same problem! My solution has been to get wider shoes and a half-size larger than my smaller foot.