I'm still not an expert on Enneagram so I can only speak from my experience/limited knowledge.
I think it depends on the way your tritype is balanced. Depending on how strong the 8 pull is, I think you could indeed get a very different looking 4. I think the different types can reinforce inclinations as well as contradict one another (creating a push/pull effect). It also depends on the instinctual variant. The sexual and social instinct seem to draw people outward; the self-preservation instinct, inwards.
I offer myself as an example.
I'm 3-5-1 (or 5-3-1?) sx/so, INTP. I'm inclined to introversion and protecting my space. But I also have the need to come out of that space every so often. I'll try to show how I think the different factors stack and reinforce/contradict one another in my world-view and behaviour:
MBTI-wise I feel like I am always doing battle with my Si. It is my tertiary and I know that there is some part of me that would prefer the security of the things I know. Knowing this, I will consciously make the decision to make myself uncomfortable in order to obtain new information (often about myself and people—Fe inferior pull, I think).
Enneagram type-wise: There is a conflicting push/pull between 5 and 3. 5 wants to go in; 3 wants recognition. In order to get recognition, I have to make myself comfortable amongst people. But since I feel safest and most at peace when I am detached, going out to meet people all the time drains me a whole lot. Reconciling my detached, safe haven inside my head with the demands of the world outside is a perpetual battle. I think in terms of bridges—I live on an island but am compelled to build bridges to the outside world. I think this is the result of 3/5 modifying one another.
Furthermore, I see 3s described as having a diminished idea of who they 'really' are. I do not identify with that. Perhaps this is because I am 3w4 but I think the 5 comes into play, too. In my detached world, I do not need to explain who I am to anyone.
Enneagram and instincts: Finally, the preference for sexual instinct—again. A pull out to people and the environment. I want a connection. I don't want to have to go through all the small talk-y things. I hate that. But I love it when I click with someone and feel compelled to go out and find compatible people. I pull them into my inner circle if they let me. If the connection is just right, they are no longer a drain and my pull both inwards and outwards reaches an equilibrium. Thus, I have very few actual friends. I feel threatened so easily. It is no surprise that my partner is a fellow INT(J) and has a 5 in their tritype.
I hope that was informative…and not just tl;dr

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