The break down via WEBSTER on the two words:
ON:
( is a function word in this case, to indicate the location of something /
as a whole it's a Preposition )
SITE:
( it's a noun, i.e. a spatial location, a place, scene or point of an occurrence
But wait WEBSTER did have a definition of ON - SITE:
( at a particular place especially of business . printed on-site . on-site day care .
on-site inspections . on-site parking )
My point here is ON-SITE is not remote.