The other night, I had a dead on HO opportunity with a bomber for the first time I can remember since I started this game.
For grins, I decided to make it as straight on as I could. I dove and leveled in front of him. All I saw was -o- in front of me, I was pretty much perfectly inline with his fuselage. He saw me all the way in though, and we both caught a face full of bullets.
I find to be safest attacking bombers, you want to introduce as many different elements into his shot as possible. Attacking from high, or if you have smash, low, and between the 2 and 4 lines or 8 and 10 lines gives him the most problems to solve to hit you, as he needs to lead you and also account for the change in impact point from his plane's lateral (relative to the gun) motion.
Nowhere is truly 'safe' if he sees you all the way in, but the more factors you can give him to work out, the better your chances are I find.
If I'm feeling lazy/having a bad gunnery night, I'll just come down from almost straight above them as a second choice. The top shelf gunners will sometimes eat you doing that though.
Wiley.