Thus a tank with a 300m range radio and a tank with 500m range can communicate up to 800m away.
Erm, that may indeed be how it works in the game, but surely that should be a bug?
The maximum range for communication should be equal to that of the lowest participant in the communication. For example...
If Bob has a radio with a range of 300m, and Mary has a radio with a range of 500m, they can both communicate with each other (bidirectionally) providing they're within 300m of each other (as radio ranges aren't cumulative in the real world)
If Bob see's a tank, then he can tell anyone within 300m of him where it is and what it is. If Mary sees a tank also, then she can tell anyone within 500m of her where it is and what it is. Realistically though, Bob having a 300m range and Mary having a 500m range shouldn't mean that they can talk 800m away. That would suggest that they both actually have 800m range.