From: Bristol, UK
You method is largely what I do too. Twins seem to be reasonably good at units, and perfectly adequate at airfields, ports and Railyards. I generally prioritise GA over GS, with a 2 layer approach... Bomb units with the 2e, and then interdict in a Separate GA AD where I am attacking. Each one gets say 20-40 bombers per hex radius (try for 20+ for a rad '0', 40 for a '1' etc.) The GS then gets what's left.
Again, no clue if this is optimum, and you need many more interdictors in poor terrain...
I have a cunning plan, My Lord