Would be interesting to see if that is why mb works, though. (Athough I personally hate it, apparently others are finding uses for it?) Of course, then the issues described in your post come into play.
My reasoning for the properties of cew's in plastics is that by adding weight to the bottom of a bey they lower the centre of gravity. But then, my main focus in that is their "anchoring" effects on their own beys movements, such as why my metal grip has very little movement.
Though seeing as this isn't really a question I should probably have pm'd you it. But with my net playing up so badly, this will have to do.