I am looking for some input on Ease Factors for fastcasting rolls in situations where using an opposing Initiative total isn't feasible (reacting to an attack the magus is unaware of, being the most obvious).
How difficult should it be to react to an arrow being fired by an archer you can't see? How much, if any, should the EF change if you hear the shot being fired? How about if the magus doesn't know who the arrow is being fired at? (That is, he hears the bowstring twang, but since he doesn't know if the arrow is being shot at himself or his buddy, should fastcasting a defense for the buddy be more difficult a reaction than for fastcasting his own defense?)
Any and all thoughts on the subject are appreciated!
My personal preference would be to base it off of how much time the magus has to react. For example, if you're falling from 50 paces, you have just over 3 s to act. Considering the length of a combat round and that you can cast a formulaic spell with a fast-cast spell, a formulaic spell should take a little less than a full round and the fast-cast spell relatively minimal time. So 3 s is an extraordinarily long time for a fast-cast spell. I would give something like that an ease factor around 0. On the fast end, it's nearly impossible to react in under 0.2 s unless your muscles are really tensed up and ready to release. I would give something like 0.5 s an ease factor around 15. (I liked your 15 suggestion when I knew the distance and the surprise.) Then maybe each extra 0.3 s decreases the target number by 3, meaning you get to 0 at 2 s?
Yup. Of course, if the sniper is far enough away and you see the bolt coming even if not the sniper, it's really not that hard to dodge a single bolt. Not that I've tried dodging a crossbow bolt, but given a little bit of distance and not having to deal with lots of other things, I've found it not too hard to dodge a paintball fired at close to 200 ft/s. While that's a little below current arrow speeds, it's at least in the right vicinity. Give the bolt or arrow a little more distance to make up for the increase in speed and you're at a reasonable chance to dodge it. That is, assuming you see it coming.
Depends how "realistic" vs. "cinematic/heroic" you want the narrative to be. If you stick w/ realism, characters will die more often (or the SG will have to fudge results, etc). If more cinematic, then PC's can be more heroic, but at the loss of some dramatic tension around the table.
It's really a call that you have to make according to your feel for the Troupe.