I respect your opinion but don't you think if that were true both feet would be sliding and both feet would have the same problem? Both sliding, both having black toenails?I'd say you going up another half size will make the issue worse. Sounds like your feet are able to slide forward during hard heelside turns, jamming you toe into the shell. Half size down in the right boot with the right heel hold for yourself should solve that issue.
Not wides, but at 27.8cm and 10.4 wide I rode size 10 Ions, Imperials, and Rulers which match my Mondo. 27.8cm = 28 Mondo = 10US. His chart would have me in size 11s. My first pair of new boots were 10.5 Motos because they were on sale, only got 7 or 8 days on those before I knew they were far too big (and soft).
What I actually ride now, and have done for years, is a size 9 Ride Fuse. I can size down because it's the right boot for my foot. I've managed 9.5s in some K2s as well, and all I do is heat mold and use a good footbed that supports my arch well.
My point is I'd trust foot measurements to mondo sizing and make that the goal. If you gotta upsize from your mondo measurement, it's probably not the right boot for your foot.
Only the longer foot has a problem, the shorter foot with a few mm clearance is perfect so my thought process is to replicate that on the other side.
Anyway I've had the die jammed in the shell for a week now, and I'm going to leave it there until the season starts so I will know if it works or fails fairly soon and post back to confirm.
Another point is with my 4e width, I don't have other boots to choose from without resorting to cutting the sides out of the liners like I used to do.