Seeing as, if you always have the greater forms available, the lesser forms become useless
inficasting represents a distinct power over that specific spell, and should represent a certain mastery
Inficasting RESIST ELEMENTS should stack with prot from ele and energy buffer, representing your mastery over the elements and their resistances
This logic could be applied to any inficasting spell in general, or at the least if inficasting is useless(as it is because of the other superior resistances) it will remain unused mostly and present no real benifit
My suggestion, allow it to stack, or, remove inficasting, and make the spells otherwise, more powerful, and potent, to create a sense of mastery over the chosen school
As is, it does so if you are epic focused, but, as of now, the epic focus will always be superior to regular school focus, for the regular school focus inficasting provides no long term benifit