Pathfinder – Friendly Switch with a medium and large (or more) characters

The Friendly Switch feat says:

As part of your movement or as a 5-foot step, you can move to the space occupied by an ally of your size or smaller, which displaces the ally to the space you just left. Your ally must be willing and able to move and occupy the space in which you were.

If a large (or taller) character moves into the space of a medium-sized ally, how does it work? Is the character "pushed" to two (or more, depending on the size) of the cases? Or does it mean that, in this situation, the average character does not meet the requirements to be able to move and occupy the space of the ally?