I think that one of the most striking things about Persuasion is how little Anne and FW actually speak to each other, and yet how much non-verbal communication goes on between them (think of those early scenes where he rescues her from her toddler nephew, or realizes she's too tired to walk). For me, only two JA couples* have a relationship that's really passionate/erotic, and Anne & FW are one of the two, largely because of this sense that they are deeply connected to each other in ways that go far beyond words.

*The other being Lizzie & Darcy, of course. Whose connection, interestingly, is most apparent in their sizzling verbal interactions -- the mirror image of Anne & FW.