Small Question regarding Fires from Afar et al.

[tinkthank]

Hi there all!
Back, at least briefly, from my long absence; hope all is well with you. I am now a father, and that may mean that I will be absent yet again as RL sets my priorities now. Hope no-one minds. (As if you noticed my absence anyhow!)

Right, on to the question:

In MP, there is province X in which nation 1 is besieging nation 2. If nation 3 casts Fires from Afar (or a similar damage-from-a-distance spell) at Province X, who gets whalloped?
- The Defender
- The Besieger
- The nation with the largest army
- The nation with the smallest army
- Random
- Something else (please specify)

This involves an MP game I am involved in (the only game I am playing now, alas), and would need a very reliable answer within the next couple of days -- can you help please?

Merci!