I also tried to figure out how fatigue was calculated (before throwing my hands up and saying it wasn't obvious). On top of the things you mention I also saw weird stuff like different levels of fatigue on slaves who had the same magic paths and were the same unit type, and reinvigoration not removing all the fatigue from some of the slaves (or perhaps it removed the fatigue on some before fatiguing them for the casting, and some after). Some of this is probably rounding type differences.
All in all, my conclusion was that the fatigue calculations in the book were not exactly correct but were close enough for rough strategic planning. Use the formula you reference above (don't count encumbrance), divide by the number of slaves and that's *about* how much fatigue each slave will get.
Re: Communion/Fatigue
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