People are not answering OP's question (despite her not being online for possibly 2 years), and while it's understandable that some users have some objections toward the premise, it isn't quite entirely false. Four is what I would say emotionally imaginative and introspective on their values and self beliefs, which is kinda derivative to a head type (but not absolutely contradictory). Ti being heavily correlated to 5, doesn't seem to have at least a strong correlation toward 4 (or even any other Enneagram types for that matter). An IxTP with an Enneagram other than five seem to be influenced by other functions (particularly auxiliary or tertiary) in their stacks (ISTP 8 seems more influenced by Se than an typical ISTP still maintaining Ti detachment and impartiality). Ti is a function that does detachment fully to be objective and impartial (supported by Fe), and does so until it reaches to a

(agreeable) conclusion or realization. This is the default for Ti and explains the strong correlation to 5.
I'm a 5w4, and while more imaginative, passionate, and artistic-ism than 5w6, I'm still objective and detached with perhaps a passionate motivator or reasons for my engagements or executions. I'm unconventional and more aversive to institutional facts than 5w6 because how of restraining they are to me and potentially dogmatic without questionings (which isn't exclusive to 5w4, but it is the most common).
(If you don't wanna read my intro, go here to see the direct answer)
MBTI types probable (as implied on this thread, every mbti type is possible with 5w4 but not every is probable) with 5w4:
ISTP (relatively stronger and higher Ni usage than a typical ISTP)
INTP (Ne usage is amplified but still stable)
INTJ (Similar to ISTP in that tertiary Fi is relatively stronger and higher in usage than a typical INTJ)
INFJ (Equal between Ni and Ti)
INFP (Fi serves more as a motivator and Ne is relatively less scattered)
ENTP (Extraverted type most likely to be one and have a stronger (or perhaps as equal) Ti with Ne)