I think Se can be understood in "different" but neverthelesss mutually complimentary ways. Force is one way to think of it, but its the way to think of it in terms of its overall "lay of the land"--the distribution of objects in an area with a view to their leverage over one another. But its all the literal "external form" of a thing. Si is also the "external form" of a thing, in the sense that its sensory. Si just privileges the subjective impression of the external form. Further Si also attends to that with regard for oneself in the form of internal sensations we broadly capture as "comfort sensing." The ability to infer such states in others is based on the subjective impression of their external form (i.e.: expressions, posture, etc) and then a kind of "Si empathy" supplies in the mind of the viewer what that "must feel like" in the form of 1st person bodily experience... in other words, sensation is the "external" part, but extroverted and introverted would be like emphasis on form v state. You in essence always get both, but attention to one necessarily distorts (to the point of possibly ignoring almost entirely) to some extent the other