Essentially, the orientations are general trends among the instincts, and there are three of them for each. So the first one tends to have a more "open" disposition, and the second one more "closed", by the standards of that type. The third is a blend of the two and appears to be considerably rarer, similar to having balanced wings. These orientations are independent from stackings, but the "open" orientation tends to correspond to syn-flow, and the "closed" to contra-flow. All three can apply to any subtype, no matter what the core type is. So you can have an "open" SP5 and a "closed" SO9. I refer to the open orientation as an "a"-orientation, the "closed" as a b-orientation, and the mix as a c-orientation.
I am describing the orientations for multiple reasons. First, I want to see how far I can push this idea, to see how much use it really has. Second, from precursory usage I find that these tend to describe the variation within a subtype better than the stacking does. Better as in, the orientations are more readily observed. So a description of them might be very useful when it comes to typing others and yourself. Third, I want to round out the lopsidedness of current subtype descriptions by stretching the umbrella, so to speak.
I should say that I am also skeptical of the notion of "subtypes" as discrete. I think different people have degrees of sensitivities in each of the instincts, and the dominant instinct is merely the most sensitive. People use all three of the instincts. And the trait structure described for the subtypes are not generalized. If we adopt the belief that SX4 is the competitive 4, just for the sake of argument, what I would be suggesting is that SX-dominant 4 is not always competitive: they are not competitive when the SP or SO instincts are activated. However, because the SX instinct is dominant, they are competitive more often than SO-dominant or SP-dominant 4s. So really, I wouldn't be describing a SX 4, but a 4 when they use SX. Hopefully that makes sense, I might not be Englishing here.
Now for the orientations. Please note that it is more likely for syn-flow stackings to be of the "a" orientation, and contra-flow stackings to be of the "b" orientation, although, as I've said before, orientations are largely independent of stackings. Also, "b" may seem less healthy than "a", but this is not the case. Furthermore, orientations are independent of enneatypes, so a two can be a sp.b, and a five can be a sp.a, for example.
(Sp.c is somewhere in between.)
(Sx.c is somewhere in between.)
(So.c is somewhere in between.)