Perhaps there is a will or intent aspect to balefire (and channeling in general) that hasn't been really considered before. If you are launching balefire at a person, your intent IS the entire person. If you miss, and hit a wall, your intent isn't the structure so the wall just gets a hole in it, if you hit the person, the floor is untouched because you only want the person. There are other hints to an intent factor in channeling particularly when new channelers suddenly do something that they didn't know they could (Avi and the gateway, Rand in the Stone)

If this is so, then there would be a power consumption for not just how far back in time the thread is burned, but for how much area/threads were being effected. Hmmmm Calculus anyone