Miners might create more than one account on more than one pool. I don't know if that is being monitored by Minerals and do those people's hashrate is being summed up to see if they are abusing the system. And this might go way beyond 300mh/s...
6 pool 50mh/s limit each, should be 300 even if they abuse, unless you can make more account for every pool, which make the whole limit of 50mh/s truly pointless..