VRay Toon Opacity problem

I have some planes that are joined together but seperate in such a way that with vray toon you get lines forming between them. I want to hide these lines using a map in the toon opacity slot. Strangely with a completely black map in the opacity slot, the toon lines are still faintly visible. Switching off the vraytoon environment removes the lines… so its not a smoothing or material/lighting problem.

I’ve managed to get round the problem by copying my opacity map into the width slot so the lines become infinitely small… but I would have thought a black map in the opacity slot should make the toon lines completely hidden without having to do this?