Machinegun vs planes in NFP

I’ve been playing through some of the NFP scenarios and had a thought about how machine gun units perform ground attacks against air units. Why are machine gun units attacking air units the same way they would any other unit? It seems like they should either roll an extra die or hit on stars during the combat roll, given the nature of machine guns. I’m planning to try this rule in my next few NFP scenarios and will share my experience afterward.