It sounds like you are using a unicast type logic. Does your network stack/game engine/game logic allow the concept of multicast? Essentially with this method, as a player zones in they "subscribe" to game messaging occurring in that zone. A player performs an activity such as an AoE. This would have a target location with an impacted area. The game engine would decide who is impacted and how, then package that in to a multicast message that all clients would receive, but that message would include a client id list and only clients in that list would process the message.
Either way, if it really was their badly programmed concept, the allocation of ports, could be solved with simple a load balancing.