I've always been more confused about how non-regenerative shields lose integrity steadily while under fire. You'd think an energetic barrier would be all or nothing - ie. at 100% right up untill it took a hit big enough to overload and knock out the shield generation system.
Is a deflector shield a sort of matrix form like a transport pattern? If so, once formed, does it deflect all energy input, including that intended to re-inforce its matrix? I can see something like that degrading as per usual dramatic ramp-up in trek battles.
You could also see how things like ablative armour (which you'd hope could be replicated in place if its worth much) and holo-armour would be a sort of progression from standard shields - something similar, but condensed down into a layer right on the hull.