I'd like to assume that those tees are the men's vintage fit, which are slimmer and much softer, just like the new retro EPCOT Center one that is for sale at MouseGear. I purchased a Small, and it fits me fine. (I'm 5'1", and very very petite). Usually, the regular men's shirts in a size small are too big, like the yellow EPCOT Center retro shirt or the black one with the multiple EPCOT Center logos. The men's vintage fit is pretty unisex, especially more than the regular standard men's shirts.
Hope it helps! :wave: I'll be at MK tomorrow, so I will double check for you.