Navmesh Pedestrian Crossing

Hey,

I'm basically creating a small town in Unity, with streets and roads and all, and there is a definite set of NPC characters moving around using the Navmesh.

Now, I don't want them to walk on the road - I want them to only walk on pavement and on pedestrian crossings. When it comes to pavement, it works perfectly, but I encounter a problem when it comes to crossings.

Basically, crossings are planes (with a cut-out texture) placed slightly above the roads. And it seems that somehow, crossings planes being to close to the roads sort of cancels the navigation baking of the crossings.

Are they any known work around?

Thanks.