The dance works fine-- I'm not sure where the confusion is.  Partner swing is on the side of the set, so one petronella means you're facing up and down the set, next to your partner.  A CA twirl then makes you progress.  1s and 2s are indeed across from each other when they swing, which is almost always true when you swing your partner, and when 1s and 2s are across from each other, you're on the same side of the set with your partner.

In other words:

"1s and 2s are across from each other to swing, and when they finish."  Yes.

"A petronella would put your partner on the same side . . ." No.

-Dave