I say they could be reaction control thrusters. Yes, I know they don't in any way fire off to the sides to be proper reaction control thrusters, but it could be that the vectors are manipulated with force fields. Ever wonder how a ship like the Enterprise (any of the Enterprises) applies reverse-thrust with its impulse engines, when the only impulse engines it has are at the back and none at the front? The only......ONLY......way to be able to do this is if the impulse exhaust is re-vectored at some point outside of the ship so that it traces the path of a square bracket " [ " using force fields. If impulse exhaust can be re-vectored like that, I don't see why reaction control thrusters can't.