I'm not 100% clear as far as how the shell changer the sound. Maybe it doesn't matter, but in my head a micro-shell equates to some type of compromise, however minor. That could be totally wrong for all I know.
The only thing would be if the BA driver was vented, then it would need more room to "breathe" so to speak. But not many armatures are vented, and the ones that are tend to be larger like the Sonion 2015, usually used for bass or perhaps mids.