Which Is More Fair ... ?

A small person and a tall person are seated next to each other on an airplane. Is the tall person entitled to sprawl into the small person's space (since it was only by chance and not by any virtue that the small person has enough and the tall person not enough space)? Or should the tall person feel confined to their own seat space (since both paid the same amount of money for the same amount of space)?

I'm not at all sure there's a definitive answer to this question. I only know I'm grateful when the tall person seated next to me takes the latter view rather than the former.