Regulated for what size person? The average ( then still too small for a good proportion ), or 60%, 70 or 80& of average? Also people are different proportions

Regulated for what size person? The average ( then still too small for a good proportion ), or 60%, 70 or 80& of average? Also people are different proportions - length v body, top versus bottom part of leg etc. You might also deprive diminutive people one of their few perks - cheap and comfortable air travel :-)