having more than one in a territory supposes that these are organized like armies… rather these are fixed deployments of batteries of grades of high density flak or weak defenses. The game treats them like some kind of ON/OFF light switch, but in each case the number of these emplacements fluctuates greatly. This is why to model them you need ‘LEVELS’ of defense… look at them like how Rommel wanted to fortify the beaches of france to prevent invasions… the idea was how much commitment of resources would be allocated by the Todd Organization to develop the various traps, barbed wire, gun emplacements, mines…etc. I view flak artillery defenses similarly, where you make investments over time to develop these. If they are cheap players will really buy this and build up the flak levels over time, rather than chuck out 5 IPC for another roll.
I think you want something more simple… rather than 1 die per 3 planes, 2 die per 4 planes thing.
Perhaps a hybrid of both is possible:
planes roll out SBR results first, then flak rolls are performed…
level 1 = 1 roll @1 (plane returns to base but is not destroyed-considered damaged)
level 2 = 1 roll @1
level 3 = 1 roll @2
level 4 = 2 rolls @2<
level 5 = 3 rolls @2<