I would like to add to Fhtagn arguments.
My point is Paris' argument is not acceptable, because the blasted individual need not be in range for a PoF-like spell. You could create a fire in a damp stone tunnel that last for a Sun duration, (sustained by magic) .When people "just happen" to try to get through, you would need to penetrate their MR to burn them.
A Pilum of Fire is just that: it create a fire that does damage. The fact that it take the form of a Pilum and need to be throwed, is just cool and is a cosmetic change.
The exemple of the PoF proove the non-sense of a reading of wards not needing to penetrate, and also the non-sense of deniying wards the use of Arcane Connection if you follow the core book rules. That's all true if you want to make a good reading of the rules. If you want to continue playing according to your view of what is a ward, I think it's perfectly fine to do as you wish.
About that part, I've written something that may add light to the comparison between wards and walls.