How about ENY affecting zones rather than whole arenas. Most times it isnt the fact that there are 30 more people on the team, its that they all are at the same base.
Way it is now:
Arena: Bish 70 Knit 65 Rook 115
Base A1: Bish 0 Knit 30 Rook 65
Base A35: Bish 0 Knit 30 Rook 10
Even though the 10 rooks were willing to leave the hord and find a fight elsewhere, they are penalized with ENY,even though they face huge odds at A35.
If it were a local ENY, the knits would face an eny hit at A2 as the rooks would at A1.