Imported items dont effect Nav mesh.

First, thank you for reading. second, whenever i import a .fbx file from blender and add it to my world and then re-bake the nav mesh the imported item has no effect on it. i cant use a nav mesh obstacle since my object is a rectangle and the nav mesh obstacles are a cylinder and it causes a little pocket of space to where the enemies cant touch the player. is there any way to where i can make imported objects effect the nav mesh?