You're right about how many players will shoot any tank any time, but for me it depends:
* Who is in the tank?
* How many blue hangars are left?
* Who are the other blues?
* Who are the other reds?
Having one set way to handle a situation is foolish. There are some tankers who you know that once they are in range you will lose hangars, while others will be sure to pick off planes. There are several tankers who I would not leave for blue noobs to take care of unless I'm sure they can't get in range before I can get back. I will often "soften" a red tank at mid field by getting several hits but avoiding the kill, trouble is someone else may have already had the same idea....oops.
Some teammates will communicate well and let you know if they are on last approach. It would be handy to set up a shorthand system, something like "......" then "...." then "..." to indicate how close you are. (Of course that would only work with blues who pay attention to team strategy.)
The tank dynamics of btc games are quite different too. Sometimes the position of the ship in the lake makes it so a red tank can't get in range for a while while other times if they successfully take out one defending plane, they can be a big problem.
Remember to cut some slack for noobs and just for everyone in general... you don't know what's going on in someone else's head. I've seen people go ballistic over miscommunications or on low levels for making mistakes that everyone has made before. Why stress?