Problem with convex Mesh Colliders

In my Project. I created many littel Planes one right next to the other by Script with different corner Positions and with Mesh Colliders on them. Now the Problem is that i want to detect those Colliders so i have to turn them to convex and is Triggered but now the colliders aren't correct even though it is such a simple object.

Has anyone encountered the same problem and if so how was it resolved. Pls answer.