The ball is not completely up the ramp in a pinball game

Hi, I am new in Unity . I'm trying to make a pinball game , I have my ball with his spherecollider and rigitbody and it works fine , also I have my paddles hitting the ball well , and imported 3D models that are convex channels through which the ball travels very well within them, my problem came when I import models straight ramps, in them ball single up the middle of the ramp , it seems that collides with something and then falls by gravity , never achieving the ball to travel the full ramp even when the force inertia is more than enough to do so .

Now try a simple elongated angled and rotated cube, and played with their fullsize collision mesh but with e same result set.

I understand it must be a problem in normal and vertices in the mesh collision .

How I can fix it?

I'd have to readjust my imported mesh objects?

Or would have to create meshes from scratch with code ?

What I can do?

thank you very much in advance for your help.