where the distances are measured from.
Good question... from my observations I believe they're measured from the unit flag. Often there will be part of a unit "in range" ie you get a green arrow over the ground, but red over the unit, until the unit flag comes within range, at which point the cursor goes green. So although individual men may well be well within range you still can't target them - this is especially noticeable when playing with large/huge units.