It seems the OP is judging his negs by look and not by performance at producing the print but having said that, then if 6.5 mins is OK with continuous rotation at the same EI as the OP uses then it suggests that his 7 mins with 10 secs agitation at the start and only one inversion every 30 secs by comparison may not be enough as I said.

Of course he has to act on what we have said.