Well, if you find somethin in the posted clarification that definitely says if stacked focus (p.84 street magic) must or must not be considered as two separate foci reguarding the bonii granted, please could you explain it ? because I don't get it.
I guess it does count as two separate foci, but I can't prove it, and I wouldn't find it really unbalanced if it doesn't, reguarding the guy with a power 6 plus summoning 6 stacked focus will pay more than the same with a summoning 12 focus.
EDIT : I can't either find how stacked focii count in the max foci a mage can bind or activate.