This came up a while ago in our group, in discussing how it's impossible to "paper cut" someone to death in the Ars combat system - that is, doing a +5 touch fire spell will only give someone a -1 penalty; you have to actually do 21 points of damage in a single hit in order to kill them.
To me, this sounded off. So, I went to investigate. The first thing I discovered is that, according to the AM pg. 116, under the "Spell Damage" header - "Many spells have damage listed in the form +X. This is an abbreviation for stress die +X. The damage inflicted by such spells varies from one casting to another." OK - so spells on average do 5.5 points more than the listing, with the potential of open-ending. Cool.
But also, in looking at the Wounds section, (pg. 178), "The character suffers a penalty to all actions (rolls and totals) equal to the sum of all penalties due to his wounds..." In this context, "Totals" seems to refer to Soak Total - ie, how well the target can resist damage. So if a character has -5 wound penalties, a 1 point wound would do 6 points of damage, and thus a Medium wound. Someone with -20 wound penalties taking the same point of damage would die.
Is that how it works?