Wow, I'd never considered that before.
Makes me think...
I've heard that some rural counties struggle to convince even one insurer to offer policies on the ACA marketplace. What's to stop someone in one of these counties with just one existing silver plan on the marketplace, starting a new insurance business, and offering a second plan with a crazy high premium, like $5,000 per month? That second plan, being the second cheapest out of two, would then be the benchmark for all the premium subsidies. This would cancel out the premiums on the existing plan for anyone under 400% of the poverty level. But if you do enroll in that expensive plan you'll pay a modest premium after subsidies and also at the end of the year the insurance company would say "Whoopsies, we charged you $5,000 per month but the claims we paid out were a small fraction of that. Sorry about that! Here, have a $50,000 refund." Seems like a great way to get some federal money flowing to the pockets of the people living in that rural area.