Folding bike like a Brompton size is an adjustment rather than a separate product..
Bullet Cargo bikes for example , are a one size product there are telescopic bar masts and seat posts .
both use one building jig so sizing is by other means ..
but it seems
like you have one,..
Bike Friday's
OSATA fleet bikes are unique in their length adjustability,
so that offers a way to change the reach /top tube length .. and height of stem & seat..
....