I'm starting a new game of AM and the question of the relevant spell level came up.
most damage spells from the CRB seem to take the damage from the guidlines, and after that, add target, range and duration modifiers.
So i talked with my troupe and decided that we'll use that logic for most spells, like "opening the intangible tunnle" or barrier spells.
the reaoning being "why should a spell affect its targets more, when it affects more targets from further away?"
Has anybody experience with that and is it a bad idea?
You are doing it how the core does it. Note that most of those Vim guidelines include bonus levels, often +10 to account for Voice range.
EDIT to add example Maintaining the Demanding Spell:
Guideline General: Sustain or suppress a spell whose level is less than the level + 2 magnitudes of the Vim spell
For the standard Maintaining given in the core book this +2 mags accounts for Touch range and Diameter duration. a level 20 Maintaining will affect a level 20 spell or less.
If you want to make a Moon duration Maintaining then it only affects spells of Spell level - 2 magnitudes because Moon is 2 higher duration levels than Diameter. a level 30 Maintaining is needed to affect a level 20 spell.
And some guidelines list their standard RDTs such as the Ward spells. Note at the end of the guideline it has "(Touch, Ring, Circle)" that means the guideline includes those and you need to determine what changes are made if you deviate from those standard RDTs.