The problems I've ran into using scaled down characters all relate to the wonkiness of the shadows a reduced scall causes. How are you avoiding that? At most, I've only scaled human characters down slightly, with no issue.

Thinking outside the box, have you tried keeping the fairy at 100% and scalling the 'regluar sized' characters up 90%? It might be a work around for you... Should also avoid any strangeness in the shadows