[lcoreyl]

My suggestions:

1) get rid of the surgical tubing just to remove that as a variable (for this test anyways)

2) try (insert compressible material here) on the wall

3) play with the compression through a full range of barely grabs the disc to "whoa, you sure you want to compress the disc that much"?
-always shoot enough that you KNOW it is repeatably bad before moving on

repeat 2 & 3 with different materials

The disc slipping on the wheel AND the disc slipping on the wall are different variables and you will want to have an grasp on their effects to your shot.