Try this tutorial, Seaspray.
http://www.youtube.com/watch?v=KRzOpUpws3sThough, if your planes are 100% perfect and 100% straight they should collide because the heads will want to take up the same space at the bottom and top. This could happen if your poi are both spinning on exactly the same plane in a butterfly regardless of whether or not that plane is straight in relation to your body or not.
While you're doing the butterfly, I find its best to have one hand over the other one, with the hand on top slightly further forward than the one on bottom.
I'd say that this is likely more the issue than your planes.
Gooooood luck!
