Hello colleagues

For my current project, I have to accommodate proper radius on concave curve to prevent belt lift-off. I am really limited in space, so I have to use hold-down roll, there is no really other choice. According to calculations I still have a lift-off issue in "empty belt" case. What the minimum material level on the belt is acceptable when hold-down roll in use? Could you please suggest any info source to refer this kind of calculations?

Thank you for any help

Have a nice day ■