The current set-up definately has its problems, many of which were predicted a long time ago.
I also think it is going to get worse because of the start of 'squeaker season'.
One thing for definate, using ENY restrictions to encourage side swapping is an outstanding failure in the multiple arena setup.
What it has encouraged is arena hopping.
Unfortuneately I can't see an answer to it

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Can usually get into the arena where the rest of the squad is, even if it takes 5-10 mins sometimes.
Had the same problem of I can get into the arena were country has numbers (and ENY'ed), but not into the one where we are outnumbered (other country(ies) are ENY'ed)
Was suggested a while ago if you want to go into an arena where your country is the lowest in numbers you should be able to by-pass the cap.
To make this work side switching may have to be disabled though (for obvious reasons.)
Still think we also need an auto-logoff after 30 minutes for inactive guys, they affect ENY for all countries irrespective if on the high/low countries.
An example -
A few early mornings ago I switched to Knits so I could hit Rooks.
Including me Knits had 6 players v 14+ for each of the other two.
After a while Knits had dwindled to 4 players, other two countries to around 10 players.
Out of those 4 only 2, me and MakoShark were 'active'.
So although it was by numbers 4 v 10 v 10, in reality it was 2 v 10 v10, of course out of the 10 how many where actually there I don't know.