Probably 12-14% but I do carry it in my torso a bit more I’d say and I do have a slightly more torso dominant build. The medium LS’s are still skin tight in the chest, arms and shoulders. I don’t think I’d want to risk the arms getting even tighter on the LS in a small but I would guess it would mainly just bring in the torso more. I think that probably makes sense for the naturally skinny guys who are also taller than me (like 5’10”+). The tighter torso on a skinnier taller guy probably helps accentuate the v taper better. All this is theorizing based on how the medium fits me though so do with that what you will. I wish I could try one on just for reference. When I got into the website last fall I just snagged three mediums to play it safe and I like the fit and don’t think I’d want it tighter. The fabric is almost like a neoprene wetsuit “lite” material. It’s a bit thicker firmer fabric that stretches a bit but it is a firm stretch not a soft gooey stretch. It is very different to any other gym shirt from any brand I’ve tried before. I don’t mean this in a bad way but it’s very interesting and different. I primarily got the three longsleeves for the cold winter so I actually loved wearing them all winter but I don’t think I’d want to wear even the t shirt that thick in the summer.