But you don't need a conductor for mana to go into a magic circle you're standing on. In the spring prayer ritual in Haldenzell, they had their regular shoes on, and the mana still went into the stage without any problem, with such efficiency that it made the laynobles pass out. I can't imagine that the very circle meant to test Zent candidates would be inferior in design to one used for prayers in a duchy. Furthermore when Rozemyne watched her first graduation whirl from the stands, she and Ferdinand saw the magic circle activate too (albeit it wasn't visible to non-Zent candidates), even though none of the dancers was wearing feystone shoes or offering mana in their prayer song.

The feystones are not a necesity, but a crutch, to make things easier for those who don't want to or can't offer mana in an earnest prayer, while whirling. Rozemyne even deliberately avoided praying, during whirling lessons, so she wouldn't accidentally activate the circle.