Having in mind the distance a hex represents, I think it is just fine.I find that the AD units are not really effective at all. With a range of 3, they still will not cover out to the 3 hex range. Mechanized AD units also only cover to a range of one hex. I liked PG2 better- AD units shot at everything that attacked a ground target within their range. That does not happen here.
On the other hand, one could expect this behavior on Artillery support (but with limited effectiveness perhaps?)