Just some ideas:
If bombers had a second larger aoe ring, e.g. doing 75 damage, they'd be able to kill all engies in at most two passes. The inner circle ring size could also be nerfed try and keep balance vs large armies. Now, if a bomber drops 4 bombs, it either gets 2-4 kills instead of 0-4. It's more consistent but not 100% predictable.
Another change, instead of increasing second ring size, is to shrink the inner aoe size and adding partial tracking to bombs, so they always hit with at least the weak aoe against engies. Bombers would be a bit worse against groups from the smaller inner ring, but hit more consistently.
One of these could also be combined with engies having larger turning circles to be worse at dodging, then maybe aoe wouldn't need to be changed to hit.
Keeping an inner damage ring with the same damage as current bombers would help to maintain current balance against larger, stationary, or unmicroed targets.