So page 79 gives Form Bonus as Form score/5 (rounded up) while while under Magic Resistance on page 85 we're told that Hermetic Magi have a base Magic Resistance equal to their score in the Form most applicable to the spell cast.
Is the Form Bonus on page 79 only applicable only to mundane sources related to that Form while the Magic Resistance derived from a given Form Score (as described on page 85) is only applicable to magic?
Just clarifying. My impression of the Form Bonus: Form Score/5 (rounded up) was that it is used for resisting both mundane and magical sources.
Form bonus is only against mundane threats.
Read p 77, The Hermetic Arts.
Technically I would say this.
Magic resistance derived from a given From Score is applied only to magic.
Form bonus adds to an appropiriate roll, but not to magic resistance.
For example, a magus with a 12 Corpus score gets 12/5 ~ 3 to soak for being punched in the face.
A magus with an 8 Mentum gets 8/5 ~ 2 to rolls involving guile or charm.
So, it is possible that both can apply in certain situations. A magus with a 4 parma and 13 Ignem has a MR of (4 x 5) + 13 = 33 vs. Ignem spells. If that roll fails and the magus is affected by the spell, then they would get 13/5 ~ +3 to soak the fire damage.