[Rupert]

To make magic attractive to at least some people in such a setting, one might want to make the HP lost count for more than a single FP each (but all the energy must be used at once, in a single spell), but keep the cost reduction from high skill at its standard amount.

This would mean that highly skilled casters (Skill-15, 20, etc.) would still cast low-energy spells for simple utility (and doing so with a range of would be a sign of skill and probably status). However, most casters would only cast when it really mattered, but because they'd have a fair bit of energy for even a 1HP cost, their spells would be quite impactful. Most mages wouldn't cast often, nor would they cast many spells when they cast at all, but when they did cast, you'd better take notice.

Add in being able to pump effective skill with energy, as you can with ceremonial casting, and maybe being able to sacrifice things and use their power, and mages become really frightening and disturbing.