There must be a thread like this already, correlating just these two, but I didn't find it so soon.
From a book I looked in today (The enneagram basics book), I got:
Type 1: Te
Type 2: Fe
Type 4: Ni
Type 5: Ti
Type 6: Fi
Type 7: Se
Type 8: Ne
Type 9: Si
It does seem like there is some Ni in type 4, right? Also being the most inside themselves... And the 5w4 looking for the image that expresses it all. I think these correlations aren't bad, although it's the same as with all correlations (they only partly align). It explains why an INTJ would be 4 (primary Ni) just as well as six (tertiary Fi); the 5-wing or dominant will be their T. And an INTP 9 would be explained by somehow being more into their Si, and why integration towards 8 would make a 5 use their secondary Ne more.
It even makes more plausible the case of a 5w4 / 4w5 being Ti Ni or Ni Ti like Jung or Nietzsche. (Marking the additive value of correlating).