How premium (2+1) boxes work?

Hello.

So i have master account and 3 game accounts.
As mentioned - i have premium for all game account (not master).

Since then i have premium only at 1 of 3. So to launch 3 clients, i have to buy 3 premium accounts or just launch premium window first or what?

If premium window doesn't count - i can launch more than 1 additional? )
Or its just limit increment when premium acc is logged?)

On the previous server, 2 windows were launched without premium, and three with premium. You need 1 premium account to run 3 windows.

2 clients max per PC, normally.

Having 1 premium account, limit goes up to 3 clients max per PC.

Only 1 of the accounts needs to be premium.

It's always MAX 3 PER PC.

If i buy 1 prem and register 7 accounts. And all my cp play on all of this accs with prem from different PC's? Can i? Or not?