I imagine what JOHN described is to basically to create a very limited white box.
The idea is to create an area around the target with as few identifiable marks as possible. Ideally RC won’t find any on the white mat (it’s not the color that counts but the uniformity, however white has no color altering propertes and also improves lighting from the bottom) and then not model anything apart from the shoes. This will probably not be perfect though because there will probably always be some shadow close to the shoes which RC might still be able to latch onto…