Encumbrance is added to the fatigue *after* reduction for high-level mages (and even after reduction for a Communion). Enc. also affects every hand-to-hand combat BTW, especially for tramplers.

In dom1, a drain dominion increases fatigue when casting spells on the battlefield (+10 % fat for every drain level) and positive magic level in the province reduces fatigue (-10 % for every tick). Exemple : in a +2 magic province, Marignon Initiates can cast Will-o-Wisp for 84 fat. only (base 100, -20%, +4 enc.), in a -2 drain the same spell makes 124 fatigue points (base 100, +20%, +4 enc.).

In dom1, extreme temperature does affect unprotected mages too. It increases enc. (added to fatigue) when casting spells (+1 enc. for every cold or heat level, if not immune, or even +3 enc. for every cold level if cold-blooded). Exemple : in a +3 cold province, a cold-blooded lamia queen has an enc. of 15 (base 4 + 9 for the extreme cold). In the same province, a Mystic has an enc. of 7 (base 4 + 3 for the cold)...

Its not changed for dom2 I think.

Cheers