INTJ Ni vs ISTJ Ni

Hello. I've been researching differences between INTJs and ISTJs and noticed that they have many similarities in cognitive functions (they share Te and Fi). Si is ISTJ hero function and INTJ demon functions while with Ni it's the opposite. The question is: how strong is ISTJ's Ni compared to INTJ's Ni? I read blogs of two people: one very often goes into futurologic theories and the other one's posts are about the present with many references to the past while his future-themed posts described only short period of time from present time. This made me think that the first person is very likely INTJ as his posts are mainly future-oriented and the past is only referenced sometimes, the other person is more likely ISTJ as his posts analyze the present with comparisons to the past and his future prognosis is short-timed. Does that ISTJs can't be as future-oriented as INTJs and their Ni works for a short time span?