Just for fun.

Don't get offended. Don't call it science.

Just call it what it is.

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• Taebaby, demure and folding his hands, waits modestly for affection, especially from Min; on the receiving end. Looks lovingly down the line to Key "umma" with whom he shares a similar role. The act of putting your arms around someone is both an affectionate and a possessive physical display - he is the only one  who doesn't do this; not because he doesn't feel these things, but because he doesn't feel he is in the position to "possess," due to his age most likely (Key doesn't do it, but still touches Jonghyun's body, whereas Tae touches no one). His clenched legs and hands: Taemin may like his hyungs' affections, but he is not easy.   
• Minho twists his thumbs together anxiously, perhaps a signal of arousal. Territorially "claims" Taemin the minute Jjong's fingers touch Taemin's shoulders by putting his arm around him (only one arm as compared to Jonghyun's "double"). Still, he keeps an elbow on the other (most likely) seme, as if to say "we're cool." He likes to around with all the guys - as long as Tae remembers who's most important. His open-leg posture is obviously masculine, the position of his... "stuff" uninhibited and prominent, a silent way of saying he is confident in his ual choice/practice.
• Jinki goes way out of the way, moving past Jonghyun, to touch Key's... lap. Even though there are others closer to him. His bias is clear. That he sits on the bottom, excluded from the "line" could mean he feels more insecure and not included as the others. Or, it can just be that the PD put him there.  :P  At any rate, he feels comfortable enough to lean back into Minho's open legs in order to get to his target, perhaps suggesting that he knows he is in charge, regardless of "pairings." Alpha seme?
• Jonghyun the skinship king, just wants to love and be loved by everyone; he's confident enough in his skills. He is touching every single member in some way (probably wishes he was alpha seme). RE: the leg-crossing, it's commonly believed that leg-crossing in males is a sign of dominion and /declaration/challenge (to other males). It's a gesture that JongKey not only share, but pretty much do at the same exact time. They also do it in the same direction, with the same leg (had it been in a direction away from each other, it would suggest that they repelled one another, not attracted). Perhaps as a way of letting others know they are the most important to each other? (Jinki crosses both their legs with his arm, completing image of 'threeway').
• Key wants to stay close to Jjong and holds on to his knee; but, like Taemin, allows others' affection. They are the most ually passive of the five, thereby making them the most likely candidates for uke-status (again, the only two who don't "possess" by placing an arm around another; ukes do not possess, but are possessed). Key also loves him some Key (touches his own knee)--he likes to be the center of attention.

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Sure, it could be BS, but what do you guys think?

See anything else?