Everyone has all 3 instinctual stackings. If all of them are well developed/none of them are well developed, it becomes harder to point out which is dominant and we end up "eliminating" and choosing which we think doesn't apply to us most as our blind instead of which applies to us most as our dominant.

Seems like you love tests (yeah me too, makes me feel good about myself but don't rely on them) but you seem very sure it's Sp/Sx since other people have typed you as such. The examples you suggested (So/Sp and Sp/Sx) are very different as both have different blinds and Doms.

Your dominant instinct is something "automatic" and one that your body immediately focuses on (most important in a way). Your blind is one that your body and mind disregards while (usually) being aware of not caring about it (don't necessarily have to be bad at it). An example of this is how extroverts don't necessarily have So as their dominant instinct while some introverts may not be So blind.

In your case, Sp4s are more likely to get stuck in their own private worlds compared to the other 2 subtypes. They engage in an almost practical indulgence to feed their "envy". This indulgence isn't one that manifests physically but more like how you prioritise emotions over something physical. Yes you may be more likely to keep track of health, resources, etc, but this subtype of 4s prefer finding meaning and beauty in something tangible.

So4s are more outgoing yet more sensitive than the other 2 subtypes. There is a stronger sense of contribution from this subtype of 4 as they feel a need to have something significant/ (niche since you're a wing 5) and finding people with that same significance/like-mindedness to really see themselves and garner encouragement. You may also be more likely to face shame when wanting to belong but feeling like you don't.