I don't claim to be able to type people's enneagram, let alone instincts, without interacting with them. But...
sp/so Because of their sp they direct energy internally. They may appear more contained.
so/sx Intensity is more obvious, and energy is directed outwardly. They would appear more open.
sp/so Depending on their E-type they tend to direct their energy towards that which will improve things for them; their work, their family, possessions, health, themselves.
so/sx Are all about people and direct their energy towards people and society, material things are not of much importance.
sp/so Self reliance is generally strong.
so/sx They are less independent than the sp/so's, strength for them comes from relationships
sp/so Also depending on E-type, sp/so's would often be described as warm and friendly.
so/sx Humour and charm is often a strength for so/sx's.
sp/so While they may desire close relationships they will seldom actively or easily pursue it.
so/sx Not only do they enjoy being amongst others but they want to form close connections with them.
sp/so Again depending on Etype they will often put their needs first.
so/sx As people are what matters, they tend to want to be liked by everyone. Practical matters are less important than relationships.
sp/so In a crowd sp/so's would be more inclined to hold back if something personal was being discussed. They may be less comfortable with physical contact. Basically you're looking at what they're not, that's sx.
so/sx In a crowd would tend to be engaged with other people, personal topics and personal conversations would likely not cause discomfort, quite the opposite.
Not all of the above points would be able to be noticed without direct interaction with a person but that's my take.