Felltower Rulings to Remember has gotten a few additions. I'll list them here as well as edit a link to them in there.
Like the rulings there, these are Felltower specific. Some may in fact be the rules as written and intended - they also may not be. They're how we're playing them for the current campaign regardless of any source material, rules writeups, and readings of such to the contrary.
"Paut restores 4 FP depleted for magic." The key word here is "for." You can only recover FP you spent to power magic. It will not restore FP lost due to someone else's magical spell, supernatural origin attacks that deplete FP, supernatural power that is like magic but is not actually magic per se, and so on. If you have any question on it being covered, it's not covered. Paut is a way for casters to get back FP after casting spells, and not anything else.
Resistance potions provide level 1 of resistance of the equivalent spell.
Improved Magic Resistance & Elixirs
In DF Felltower, Improved Magic Resistance provides no benefit whatsoever against hostile elixirs, nor does it hinder friendly elixirs. It merely acts as Magic Resistance against hostile magic only, and does not impede helpful spells or your own casting.
This one is not a ruling, but it is a FAQ.
Is the cost reduction for high skill on the base, or the final, cost of the spell? Final. I can't believe I have to answer this roughly once per session after 9 years of Felltower and 30+ years of steady GURPS gaming with the same magic system.
See also Protection from Evil.