Navmesh, Please, I really need a help there

Hello,the deal is about navmesh doesnt builds nice. I have a small(real-sized) train car, and it seams that nav mesh can’t handle it, even with the agent size 1! I cant change the size of the train and want to use nav mesh for teleporting player in VR. I would be happy if anyone know how to treat this. Thank you in advance!