Now, more toward the OP, as we do know things like BoAF are resisted. Since it's resisted, we know and since the Target is technically the fire created, it falls under this category for resistance:
If the target of the spell is a magical thing, which then attempts to damage the maga, the spell works, but the created thing is unable to affect the maga unless it penetrates her magic resistance.
Things that are created and sustained by magic (anything not created as a mundane thing by a Ritual spell) are magical for these purposes.
Why does Magic Resistance matter here? Because it says
If the target of a spell has no magic resistance, then he suffers its effects no matter how low the penetration total, even if it is negative.
Magic Resistance, according to the book, is about stopping these "magical" "effects." So, if BoAF can be stopped by Magic Resistance, which we do indeed see, then if it penetrates the person "suffers its effects."
That certainly sounds like the person would fall under
Anyone subjected to a powerful mystical effect gains a Warping Point
Now, do the rules say an effect must be beneficial to cause Warping. No. Actually, they demonstrate this is not the case at all. There are effects that are not beneficial that are explicitly noted as causing Warping:
Rewriting the Mind... This spell incurs Warping as a constant effect of high power. (A&A p.33)
The Penitent's Confession... This effect qualifies as scrying and causes warping, so very few magi will voluntarily submit to it. (HoH:TL p.73)
And do the rules state that the subject must be the Target to undergo Warping? No. Actually, there is at least one example where we see someone subject to the spell and specifically not the Target explicitly gets Warped:
Summoning the Spirit of Anger... Casting this spell inflicts a Warping Point on the source of the anger (HoH:S p.99)
So, with BoAF:
- We know the person being damaged "suffers its effects."
- We know "Anyone subjected to a powerful mystical effect gains a Warping Point."
- We know that it not being beneficial does not prevent Warping.
- We know that the person being damaged not being the Target does not prevent Warping.
Nothing is explicit here for it, but most the arguments against it Warping above seem weak or incorrect. To argue against it causing Warping, it's really about making the argument that being "subjected to a powerful mystical effect" does not include "suffer[ing] the effects" of a powerful mystical effect. It seems like it would take some mental gymnastics to say that someone suffering the effects of a powerful mystical effect is not subject to a powerful mystical effect.
However, I totally get people not wanting to have to track things so much and not wanting to throw an additional painful thing on top of a dangerous attack in a game that can be so deadly.