Don't worry too much about it. Tail biters are frustrating to no end, so stressing about the biting is almost completely pointless. They'll bite as soon as you think they're done.
Perhaps Chester can see his reflection, but I'm doubting it if his tank is rounded. I've only experienced a betta flaring at its reflection in a rectangular/square tank; never a curved one.
Biting is usually boredom, stress, insecurity, or aggression related. Some bite to bite and some also bite to relieve weight. I think your best bet is to keep him tired out with flaring, but also calm when he's not flaring.
He might like to chase a button around his tank, which will be great exercise for him as well.
Clean water and a high protein diet will be his best aid in regrowth.