I have seen other players who can micro the dox to dodge the tanks. But I can't figure out how to spread out the dox to dodge the enemy bomber. Another question is how to use dox against bomber. Sometimes the dox can hit the bomber, sometimes they can't. Is there any elevation limitation for dox? I feel that they can't shoot the target which right above them. But I am not sure.
Yep, you use area patrol to dodge the initial shots, after that you pray harder than you ever have before. That said, you can also use the "cover the line" mod to spread your dox out but it's only really practical for dodging the initial bombs. Area patrol requires little micro and generally does a better job of keeping your dox alive with the highest chance to hit the bomber. There isn't an elevation limit as far as I'm aware. Don't know about the dox not being able to hit the bomber if it's directly below it though.
I prefer Cover The Line for dodging bombs. No matter what solution you pick, you're going to need some way to deal with those bombers as fast as you can. Area patrol may require a bit less micro, but it won't save your dox any better if the bomber gets more than a couple passes. Area patrolled dox also like to stop moving and shoot at things, which makes them great targets.
This also depends on whether you have your own air force to counter the bomber(s) but if the dox themselves are how you plan on countering the bomber(s) then using a mix of cover the line and area patrol is your best option as you can use cover the line to quickly and efficiently position your dox to the optimal attack position after doing an area patrol scatter.
If you intended to try and focus the dox to keep them alive, have them run in the opposite direction of the bomber, the "bombs" fall in the direction the bomber is faceing, so if it is attacking North to South run them North. If you are just looking for serious longevity. Area Patrol.