I think most leo makers base their measurements on the length from the shoulder to the crotch. They may also factor in the measurement of the chest, waist, hips and torso. My dd fits fine in a CM (she's 6) but can also wear a CL with a little room. As far as comp. leos go, they ordered her a child small because yes, they do want them skin tight. It almost looks like they spray painted it on!

Every girls body is different so do your measurements to get the best fit.