Unfortunately, the only thing I can see as a "help" to the caps, while keeping 2 arenas growing is a "hidden" cap system, allowing for squads/matchmaking.
What I basically mean is... instead of allowing the customer to choose one of 2 arenas (and getting angry they can never get in), the system go through a logic process to determine which arena to put the customer in...
For instance - Customer signs in, clicks "Late War Main"
All logic is based on the assumtion that minimum max arena size = 150... (so if 150 is > (125% Arena#, the max is still 150)
This also goes under the logic that NO ARENAS show current and max #s, or at least only show current #s of all arenas combined (for instance, if Arena 1 had 250 and Arena 2 had 222, it would show "LWA 472")
Is customer in a squad?
Yes. - Which Arena is Majority of Squad in? 1 or 2?
1 - Is Arena 1 > 125% of Arena 2? Y/N?
Y - Join Arena 2 - Is ENY of Country attempting to be joined in Arena 2 > 5.0? Y/N?
Y - Inform user of ENY restriction, prompt if wish stay with country, or change country for ENY balance (and show ENY information).
N - Join Arena 2 Standard Country. (message: Sorry, Arena 1 Full, please try again later. Assigning Arena 2)
N - Is ENY of Country attempting to be joined > 5.0? Y/N?
Y - Is majority of squad in a different country? Y/N?
Y - Prompt if customer wants stay with country, or change to squad country (i.e. choose stay with country, or stay with squad)
N - Inform user of ENY restriction, prompt if wish stay with squad, or change country for ENY balance (and show ENY information).
N - Assign customer to Arena 1, their standard Country.
2 - Is Arena 2 > 125% of Arena 1? Y/N?
Y - Is ENY of Country attempting to be joined in Arena 1 > 5.0? Y/N?
Y - Inform user of ENY restriction, prompt if wish stay with country, or change country for ENY balance (and show ENY information).
N - Join Arena 2 Standard Country. (message: Sorry, Arena 2 Full, please try again later. Assigning Arena 1)
N - Is ENY of Country attempting to be joined > 5.0? Y/N?
Y - Is majority of squad in a different country? Y/N?
Y - Prompt if customer wants stay with country, or change to squad country (i.e. choose stay with country, or stay with squad)
N - Inform user of ENY restriction, prompt if wish stay with squad, or change country for ENY balance (and show ENY information).
N - Assign customer to Arena 1, their standard Country.
No. - Is Arena 1 > 125% of Arena 2? Y/N?
Y - Is ENY of country attempting to be joined in Arena 2 > 5.0? Y/N?
Y - Prompt if customer wants stay with country, or change to another country (i.e. choose stay with country, or lower ENY)
N - Assign customer to Arena 2, standard Country
N - Is ENY of Country attempting to be joined > 5.0? Y/N?
Y - Prompt if customer wants stay with country, or change to another country (i.e. choose stay with country, or lower ENY)
N - Assign customer to Arena 1, standard Country
This system would not only make sure the arenas grow evenly, but also give options to help with ENY, and choices to stick with squad or not. It also would stop waving those "max arena" numbers in people's faces making them obsessively click on an arena, then quit, then arenas, then quit looking for that right moment when the caps change. These caps ALSO would be much more "organic" in growth, without the harsh 50-100 person max cap limits that happen now.
Not saying it's a great system, just a different one. It satisfies the need for split arenas, gets all customers in game, and even prepares people for possible ENY cap restrictions. This is a very "barebones" system and I have a much more complicated one in my head with this as the baseline (the one in my head allows flexibility in the max cap based on ENY needs), but I wanted to at least get the concept out there for discussion.