Ok. in pic:
Green capsules are navigators in blue navMesh.
Red line is optimal path.
Gray is collision model.

Navigation mesh is made for taller navigator so no navmesh exist under ramp.
But shorter navigator actually could use navigation mesh that maps area under
bridge.

So the question is: What is good way of storing aux data of sectors
height to navMesh? (store data to vertices/edges/polygons? etc..)

/Tyrian

You generally need a separate navmesh for different sized actors. We had an FPS game with small, medium and large navmeshes and constrained unit design to fit within one of those three footprints.

-me

For what it's worth, you can handle agents of arbitrary radius using a single navmesh with a little extra work. However, I haven't tried doing this while also taking height into account, so I can't comment directly on that. I imagine you might be able to store 'headroom' information with each navmesh cell that could be used during pathfinding to plot an appropriate path given the agent's height, but I'm just speculating.