I get the feeling if you decide for straight sleeve, then you should get a wider shoulder than your natural shoulder so the jacket is a bit off shoulder to look somewhat clean around the armpit, if that jacket in your shoulder size it will look like a mess on the underarm folds in neutral pose, ( i bought my denim jackets in my shoulder size, and every time I have to alter the sleeve to be more angled to look clean with my arm down on my side, if I buy them bigger I think I can get away with it sorta like round sweater look)This is described in this thread.
https://www.vintageleatherjackets.org/threads/fivestar-leather-a2-jacket.21625/page-44#post-289143
If the sleeve is a straight extension of the shoulder, it becomes less boxy. Perhaps this can best be compared to a raglan cut. In contrast, a classic Sacco, where the shoulder / sleeve angle is quite large.
and the suit jacket is the opposite you should get it right at your shoulder size. and it will look perfect.
why would somebody prefer a clean look for a T pose, how often human pose that way, or are they leaping lemurs?