I had tested this at least two years ago when the Allied DLCs weren't out yet, but the specs already in. No problem if they aren't officially supported yet.
Now, years later and officially in the game and campaign trees of Brit and US, I'm very disappointed that they still don't really work (and no one bothers yet. Okay, I know strat bombers usually suck!

I had to wind up the large-air attack to something like 100 to finally see a scratch on a strat bomber protected by adjancent ally strat bomber. It's like the spec - Bomber Stream and Combat Box use the same code btw - multiplies the air defense by 10 or something.
The test in the screenshots below is with an unmodded game besides the increase in large-air attack.