I can still remember that RedBoy786 brought up this issue about 2 years ago on Graalians.com and if my memory doesn't fail me, an admin mentioned that it is indeed impossible to solve the problem because it's a clients-server issue (hope I said the right term).
I'm having a hard time thinking of how I should phrase the sentence, but I'll try my best to make you understand.
The issue is that whenever a holding gang member enter the door, the door would stay opened for a while and hence the enemy's bullets would be able to pass through the door although the door is closed according to the enemy's screen.
Since there's no solution to this, I have came up with a "prevention", and that is to reduce the time taken for the doors to close after an occupying gang member has walked through to maybe, an instant.
One possible complain I can foretell that players will have is that there would be more "runners". Now honestly, I don't see any problem with running.
My question is, do you fight for success or for failure? Of course Success right? (Sorry for the Dora question) Escaping and healing is part of survival and definitely part of the game. Why would you want to take the risk if dying and possibly losing the base just for the sake of proving your "courage" to an online player who could be a 9 years old kid like my younger brother behind the screen?
Base doors should be closed immediately after you enter.