If I'm ISFP, I would say whatever Ni I have is a result of introversion. That's my theory at least.. that a lot of Fi or Ti in IFPs and ITPs would go hand in hand with other introspective functions: Si and Ni. Same with IFJ/ITJ and their Ti/Fi. ISFJs may not use Ti like an INTP, but some can be meticulous researchers, fact finders, and may sift through a lot of material and bring up many reliable points in their presentations or something. And it's probably natural for INTJs to speak of some Fi, like Edgar does.
True about ISFJs; I definitely see what I think is tert Ti in my ISFJ mom. She's very capable of making a logical argument, but it's usually in the interests of a feeling.
"Charlotte sometimes dreams a wall around herself. But it's always with love - So much love it looks like everything else. Charlotte Sometimes - So far away, glass sealed and pretty." - The Cure