It has been so long since I have logged on to this site. It has been over a week. Awe man, my BeySpirit is dying.
Anyway, It seems as if there are multiple reasons as to why Upper Attack worked in the Plastic and HMS generations (Circle Upper did have upper).
Many (even I) say that it is because of the recoil of of the metal that causes an immediate separation between the two, as one hits the other, and third law of motion comes in as the other bey hits the other in a action reaction type thing, resulting in a strong collision leaving the shape of the beys useless and no destabilization. Sorry if I explained that poorly.
But, it could be the weight of the Metal Wheel/Attack Ring. In the plastic series, the attack rings usually weighed 5 or 4 grams. Because of that, the attack ring will be able to lift the other attack ring, and eventually the hole bey, as the attack ring is light. The HMS series had Upper Attack.
http://www.youtube.com/watch?v=6dkH4NMzd...age#t=175s Somewhat. No, okay, it was good in the system. The attack rings were 20 grams. So they could lift, and the smash will supply a boost. The MFB's have heavier weighting, Wheels. Or Metal Wheels. The average amount is like 35 for a Wheel, and 35 to 39 for a Hybrid Wheel plus a Metal Face. Now, that top part alone weighs the most of the bey, as where an attack ring would lesser than most of the bey, and the HMS attack ring would have the same weight compared to the other parts of the bey that have no contact in battle.