From reading everything I could get my mitts on, I learned that the fillets primary purpose was/is to provide a nice curve for the tape to lay on. Glass tape doesn't like sharp bends, tending to either not lay in it, or to break, neither of which is particularly good. It also helps nicely for holding the very edge of the plywood, where the tape isn't actually lying. So, imo, use the smallest fillet you can comfortably lay the tape into. For me, that was roughly the fillet created with a popsicle stick.

As for the wire, how far up did you drill your wire holes? I kept mine down low, which did mean the occassional tear out, but also meant I could keep it down in the filleted joints pretty easily. The use of a screwdriver to press the wire down also helped me, especially for those areas the wire was up a bit.