The bbp axle flanges are about 3/16" to 1/4" thicker than the sbp flange. So there's a potential 1/2" total. I'll measure again to make sure I'm not crazy because this is boggling my mind too.
That would be maximum. It's probably less than 1/2". So still far from 15/16"
This is a little far out, but....Do you have adjustable rear wheel bearings? Are you measuring from the adjuster side and have not made your adjustment yet and the axle is adjust way out?
Ask Dr Diff about what you ordered from him.
IMHO, you should be looking at 245 wide rubber front and rear.