Considering that this rule is currently neither respected nor enforced, I suggest that we drop it.
It would probably make it clearer and easier for everyone too. And having the field spread out(-ish) on two servers would help reduce traffic, especially on short tracks like BL1.
This rule is more like a recommendation, to avoid very slow drivers driving Q on A, and also to avoid fast drivers doing there Quali on B nagging on slow drivers at B.
The rule was added when we changed to "hard-core-quali" and there were a lots of concerns from some fast drivers that their Q would be spoiled by slower drivers.
In general I think its working ok now, but if you feel there are extremely slow drivers on A, pls let the admins know! Usually I also spam you on the LFS chat with some basic rule reminders before the Q starts, including reminding slow drivers to do there Q on B :-)