A big tire gets into Toe clip overlap problems as the top tube reach has to be shortened,
in relation to the size/seat tube length .. smaller bikes are shorter too.

but the front wheel needs more length to not interfre with your feet , turning at Low speeds

small-big is a problem.

A Nice Bike without getting into these problems : Bike Friday, & accept the Small 20" wheel .

they have a toll free number, to dicuss the needs with a consultant to get the ball rolling.
and the Eugene Oregon Based company is a flexible JIT, manufacturer,
so the Bike is made as the Order comes up in the queue. .

and will do alterations for other than the average rider .

as you have special needs , they would be the path I would reccomend ..

it will be a bike Made For You, individually.