I'm sure this has been adressed in similar ways, but...
One of the goals of the new xp/gold system was to make income indepedent (therm sounds wrong) from player numbers and game mode. Due to my experience and what I've heard from others the latter has failed. While in battle I regularly get x4 or x5 and sometimes for several rounds this seems impossible in siege because of more frequent (every round?) autobalance.
Is it really intended that autobalance kicks in more often in siege or is it just because of more player fluctuation? Either way perhaps you should give it a try and make it check only one time per map in siege. The result could be of course that there would be more unbalanced teams the longer the map is active but I think it could be better than now.
Btw are there any numbers on how much gold/xp players get in comparison of battle and siege?