2 small questions about horror mark

[Vicious Love]

I always want to make use of the incombat horror spells but am never quite sure just how compelling a horror mark would actually be ?

To the furthest of my rather meager knowledge, a horror on a battlefield will ONLY attack horror marked units until:
A) All horror marked units are dead, or inaccessible(No empty spot to fly into beside them)
B) A horror has made its move, killed a horror marked unit, and been left with one or more unused attacks and no marked units within range.

I'm even less sure of B than I am of the whole hypothesis. It SEEMS to hold true, but I've only seen horrors attack armies after summoning those horrors myself, usually after sending a few vampires into hand to hand with Shields of the Accursed the month before. Consequently, with such a ganerous marked->unmarked unit ratio, making any sort of conclusive observation was... tricky.

Update: A few questions of my own, by the way.
1) We know that casting spells and forging items is more likely to attract horrors than just kinda lounging around, even in high-magic provinces. The question is, how much more likely? Do multi-path spells or items check for horror attacks twice, as with Astral Corruption? Are more powerful spells more likely to attract horrors, or to attract bigger horrors?
2) More powerful mages seem to attract more powerful horrors. Are horrors keyed to mages' path levels, or does it simply seem this way because powerful mages cast powerful globals(And the gem cost of the spell results in bigger horrors) or end up getting more powerful horror marks?
For instance, if the Forbidden Light, which presumably incurs one of the most powerful marks in the game, were given to a scout, would that scout attract doom horrors, or would he just be very, very likely to attract the usual lesser horrors?
3) I don't suppose anyone knows the relative strengths of various horror marks? Is the Oath Rod of Kurgi's horror mark powerful enough to actually be useful without Send Horror or Call Horror? Do higher-penetration castings of Horror Mark result in stronger marks?