Quick question / observation. Seems that the Perdo guidelines require form specific effects (such as Unraveling the Fabric of ..Form) to affect magic , such as one for Corpus, one for Animal, etc. That is unless you can get double its level (as in Winds of Mundane Silence).
And the Rego effects make it slightly easier to affect your own spells, but the Perdo ones do not. However Perdo spells seem to allow a +Dice roll.
Have I missed an errata or is this just the way RAW is? Curious, not complaining.
There is a generalist Perdo guideline - it's like the specific one, (lvl of the effect + 4 magnitudes?) but you /2 beforehand. It's the one that "Winds of Mundane Silence" is based on.
EDIT...which you talk about in the 2nd line of your post. D'oh! Ah, well. No, from what I understand of this, you're correct. However, the observation is that, because you get so many free magnitudes with a lot of the PeVi effects, it's often easier to spont the effect than it would be with other TeFo combo's.
Personal favorite: if you want to learn antimagic, learn the lvl 20, touch-based version of Winds of Mundane Silence - that gives you 15+stress levels of generalist antimagic. That's actually a pretty good deal, if you learn the fast-casting mastery. (Combine it with a RegoVim sight-based Tunnel enchanted device, and you've got some pretty good countering abilities.)
Eh? How?
Opponent casts spell, you do a sight based Intangible Tunnel to what? The spell? You're fast casting that? And you also have to fast cast the anti magic spell? The trouble with that is that you have to fast cast the Intangible Tunnel to something that already exists, and at that point, it's too late to negate it with a touch range anti-magic effect.
Tunnel is built into an enchanted device, such as a ring - which activates automatically whenever you cast a touch-based spell (or "activate upon magical gesture with the hand the ring is worn on" - or something to that effect). The only real issue is "how do I detect the Tunnel, as it's being cast by a device?" So either the device needs an CrIm(vi) effect to display precicely where the tunnel is, or the caster needs to know a low-level InVi "Taste the aura of magic" - and they'll need to kiss the ring when they cast.
EDIT - or a slightly-higher "touch the aura of magic" - and seeing as the ring is the thing creating the tunnel, it's probably pretty easy to figure out where to touch to detect the darn thing.
EDIT II - although I would personally HR that the "you must see it to affect it" invisibility rule is due to the abstraction of the combat system (as is suggested in the Flambeau section of HoH) - and that a device which consistently creates an invisible tunnel in the exact same place relative to the caster doesn't actually need to be directly perceived to be affected. Or if you want to be technical - the casting effect of the ring itself (the fact that it glows, and gives off light in a general direction, vapor convalesces where the tunnel is about to form, etc.) is enough information to be able to indirectly detect where the tunnel is.