DM Fletch:
Zyphen, (going back before the Simultaneity discussion) my recollection was that when the people involved were in melee the -4 penalty applied (and could be negated by Precise Shot) but when they were otherwise between you and the target it blocked line of sight.
In part I was being lazy, in part I think the -4 penalty is ridiculously lenient and on the whole it was an arbitrary decision to impose a 50-50 luck roll. I hereby invoke my GM's privilege to be right :)
BTW, my wife is a physicist (and physics teacher) - and a chemist (yes, she's standing behind me), who would be interested in the OOC discussion and in playing. She's already on OOC as PC draco2075, so I'm going to put together a cloistered cleric for her to play - just as soon as I check to see that the variant class is allowed.
Actually, most commonly played way, I think is that when you have someone involved in melee, it's -4, as described in the rule. But also, when that someone else (or for anyone else in the way in that matter) is in the line of shot, they count as "light cover", and impose further -4 penalty to hit, and end up giving -8 penalty (Here, assuming the melee combatants line up in the melee position so that the non-target melee combatant provide some cover to the target melee combatant).
I often ignore that rule though...I like my combat...bloody (so it works on both ways ::laugh::) My perfectly designed combat will involve at least half the party member down and dying at the end of the combat *laugh*
-K