In my experience, it's actually as many players that are actually switching as it commonly seems to be believed.
Sorry didnt quite get that.
I always tend to swap over to the side with the lowest numbers (not that I can do much once there!

)
Personally I think anything that makes people wanna stick to one particular country should be discouraged. Id even be so bold as to force squads to switch countries each tour. I believe people will wanna stick to whichever side has their squads and can be an indirect means to ensure some balance in numbers.
At the moment, people sticking to one country or another seem to have caused the development of various country specific mindsets. Heres what Ive seen as of my limited expeirence so far:
Bishes: A horde for everything, and eveything with a horde.
Knights: There is no team in 'I'. If u cant do it alone, dont do it at all.
Rooks: Closest Ive seen to some sort of occasional organised team play.