Im pretty sure the slaves get the bonus too otherwise reverse communions wouldnt work so well.
Dont forget the slaves can only cast if there are no masters ahead of them in the commander order.
If this is for what I think its for then you will struggle getting through 24MR with soul slay so you will likely need a few more that 5 mages to win. Minimum of 8 slaves for +3S, Power of the spheres + Light of the northern star will give S1 masters S6 for +1 penetration castings of soul slay (every 2 path levels over cost gives +1 pen). Then add in penetration items for the masters for up to another 3 penetration (spell focus and eye of the void.)
If I remember correctly soul slay checks against MR at 12 so vs 24 MR it will only have a 2% chance of working. +1 pen gives 3%, +2 gives-4% and +4 penetration brings it up to 8% which is still not great but with a bunch of chaff and good positioning they will hopefully keep casting soul slay even after going off script. You will quite possibly see a lot of cursing and horror marking though once the script runs out as the casting AI freaks out when confronted with that much MR on a big beefy SC.
Chances of SS working can be figured out from
here
There is also a communion strategy thread here
http://forum.shrapnelgames.com/showthread.php?t=37499
Re: Communion question
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