It depends on how you view tritype, and there are two real ways of doing so.
You literally move from type to type - in your case 7-8-9-1 - as each type's way of dealing with something is unsuccessful
The types converge to form a cohesive strategy that can be situationally influenced by all types at varying times and varying intensities, but that there is a pattern towards certain types over others
In either case, your core type is what governs. If you are a 7 core, the fears of type 7 shape the structure around which the other types operate - so regardless of tritype, you are always a core 7 and operate at least via 7.
A 7w8 is double aggressive types, and will be very assertive in seeking stimulation either via ideas or activities. The 7 wants to feel satisfied, and the w8 makes it more independent and assertive, willing to fight or stick it out for such satisfaction. A 9 fix would probably soften the energy of 7w8 quite a bit, making more of a "diplomatic" feel. A 7-9-X would first want to feel buzzed, but also do a lot of self-forgetting and numbing out to dull away what results, since they can also take in all POVs. Likely an even more optimistic 7 than usual, and when things get rougher they may alternate between overthinking, and unconsciously resisting their environments through inaction despite the positive outlook.
I have wondered the same question because I believe myself to be a 7w8 but a 739 (9w8) as my tritype. I completely understand why and how my 8 wing affects my 7 core. However, I can honestly more relate to the type 9 in dealing with anger then the type 8. I would rather check my self out. I feel I came out developed with an 8 wing over 6 wing because I received more push and less instability in my enviornment as a child, however I developed more of a 9 strategy with anger.e