I am sorry, i have not used GPA and i don't know what you mean by "Primitives are far off from the ones of the Pre Call".
I think that it is best for you to hook onto DrawIndexedPrimitive() and "do the thing" in there since that is most obvious place as it must have previously set correct vertex decl. and buffer. Did you try some other games? Maybe that one have some kind of protection against these things?
My english sucks.