Well, the primary reason I posted it this way is to remove the single team advantage yours presents. If Bishops hold that field then they have the advantage of knowing when either of the other teams spawns in. It's not much of an advantage, because any team gets the visual flashing base indicator, but the Bishops would get the verbal warning as well.
As long as these bases are at least 4k separate it won't be a problem. I would suggest 5k separation, but 6k would be even better. At 6k though, someone can sit on their base and the other bases will not flash, so I would recommend that no further separation should be used. That's 6k measured from spawn hangar to spawn hangar.
Keeping these bases uncapturable will satisfy the vehicle fight may remain perpetual. Making the outer fields uncapturable would merely make it more difficult for the TT fight to return once the center fields are taken. If those fields are capturable you can bet dollars to donuts they will be captured, and then your TT fight is finished.