all i remember from going all out was how kris completely towered over chen lol but yeah, it's tricky with the angles. if you look at this picture, for instance;
http://25.media.tumblr.com/tumblr_m3pi172rq81rvuanco1_1280.jpg
chen is roughly luhan's height but he also seems to wear quite a fat insole lol, + heel of the boot. but idk it's really hard to tell whether they wear insoles or not.

also, re luhan trolling/teasing.. i think it's rather him teasing both xiumin and chen for being short. it's sort of weird to assume that he's pissed at chen for being taller or something lol.