While I do think that there should be some kind of script that keeps certain heroes away from certain units(ex +1 move for planes), I come back to the fact that every game has its unique limitations.
I use a certain explanation(or delusion) to explain heroes. Most of them center on stacking units on the same hex.
Panzer General was developed from Avalon Hill games that I, and other old-timers, know very well. I still have the complete "Advanced Squad Leader" set and "Rise and Fall of the Third Reich". Hence my handle here.
Panzer Corps is the direct child of PG.
In Avalon Hill games, units can be stacked on a hex. We cannot do that here.
For example... artillery. Arty in this game is usually "over-ranged", to make up for the lack of stack. Don't think of it as "behind" the front units, think of them as just to the rear, but still within the Forward Battle Area. On the border between two hexes if you must.
A range hero on arty is explained in my mind as a commander with the chestnuts to move his guns as far forward as possible, as well as the ability and equipment(new barrels) to project fire farther.
However, I do believe that limits should be coded in. No more than a single range or movement hero on ANY unit. My suspension of disbelief only goes so far.