I'm not entirely sure how similar Ni and Ti are in separate individuals, such as an INFJ clicking well with an ISTP. The textbook definition of Ni is a future-focused pattern-finding function, and the stereotypical Ti is fine-tuning concepts in one's mind, maintaining inner logical consistency, and solving problems. Both are highly analytical in nature, so I suppose a Ti-dom and a Ni-dom could have some fun discussions with each other. The difference between an INFJ and an ISTP as far as Ti and Ni goes is that the INFJ's ti will be their tertriary function and their Ni will be their dominant function, and the ISTP's Ni will be their tertriary function and their Ti will be their dominant function (please forgive my pairing of "INFJ's" and "their"). This will make it so that the INFJ is far more familiar with Ni than the ISTP is, but far less comfortable with Ti than the ISTP is. Additionally, an INFJ is more likely to use their Ti with their Ni and the ISTP is more likely to use their Ti with their Se which will result in some pretty drastic differences. As an INFJ, when I use Ti, it's usually to think about a pattern I've observed in myself and others. An ISTP would probably use Ti to think about something happening in the moment. The latter is just a guess since I'm not familiar with ISTPs and this whole post is just a generalization.