How to set a forward pass on a mesh grid?

Question

Unity

I still can’t set up the mesh mesh correctly, for example, how it is baked for me

That is, point A and B (red and green squares), it should move along the path of the green strip, but for some reason the path is calculated along the purple line, obviously not the shortest option, already twisted this way and that and still does not work.
The plane itself is 2D.

Tell me how to build a grid correctly, in fact, if these lines didn’t exist under which it adjusts ...