Since it only works when interacting with ground units (which to me means using the Ground Mapsheet rules) then I'd guess you'd measure from where the fighter ends its movement.
Of course, this raises a few questions
1) What about units that the Aerospace unit attacked in that turn. Are they considered at a base range of 0?
2) How is elevation handled.
3) How does things like ECM work with regards to Elevations, rather than levels?
Probably all things that should've been addressed in the rules in the book.
If I had to guess, I'd say measure from the fighter's end point to all the units, taking into account elevation as if being fired at (+2 hexes per level of elevation I think?), except for any unit the fighter attacked, in which case, the range is 0, with the same modification for elevation.
Its a little powerful (Not only did my fighter just strike you, but that Osteon is now at an incredibly short range), but it seems to be the fairest way to do it.
Best bet is to ask the writers/developers, and hope they thought of this when they wrote the passage in the book.