I did some tests and managed to use 4 ethminer running at the same time with 1 card. 1 rig with 12 gpu can get 48 active miners able to pick up uncles 

This random distribution of uncles is not fair, i agree with u, they need implement a minimum 'T" balance or something like that to stopping this fucking guy who created 7500 miners at 5mh/s.

Let's see what Ethpool will tell you.