I think it's a pretty natural way for men to sit--they tend to spread out and take up a lot of space, physically and (in my opinion) psychologically.

I'm like you, I notice and am wary of a lot of "masculine" cues. My T had his sleeves rolled up once, exposing his forearms and it was very worrying for me. I did not like it at all.

I do think it can be good to talk about these things with T--sometimes when I feel like T's gaze is too intense, if he turns his body to the diagonal I feel a lot less pressure. T is a good place to discuss how we react to bodies and space. It's practice for the outside world, to see what you are sensitive about and how you feel comfortable interacting.