I think the idea there is that generally speaking doctors get rebated on some sort of defined cost schedule. They'll get $40 from the insurance company for some basic kind of visit, and that is "fixed"...
I don't live in the US and when I did wasn't paying doctors very often... but my impression was that even if the rebate schedule is fixed they could "just" ask for more/less, and the rebate schedule is defined by the insurance company (so the insurance company can increase their costs through this schedule, leading to ways to make profit elsewhere!)
I could be totally offbase, I've always thought the Obamacare profit percentage cap to be a fake constraint.
