Specifically, according to some testing I just did via CCSM (the slider in System Settings doesn't seem to work with my installation of Trusty for whatever reason…), edge illumination is not present for sizes up to 20, for sizes 21-39 it's offset, for sizes 40-58 it works perfectly, and for sizes 59 and up it's offset again (albeit without the small gap this time).
Specifically, according to some testing I just did via CCSM (the slider in System Settings doesn't seem to work with my installation of Trusty for whatever reason…), edge illumination is not present for sizes up to 20, for sizes 21-39 it's offset, for sizes 40-58 it works perfectly, and for sizes 59 and up it's offset again (albeit without the small gap this time).