I am using this light weight setup and am wonder is this happening to others. My UR-E20 is touching the knob.

I can adjust it to be like the following, just missing both ends...

but the 2nd settings will take a picture with the lower rail in it., yes yes a nadir will remove it but am wondering the setup for now first. I tried using the full NN3 setup:

and it's hellava lighter (of course) compared to my usual 40D + 10-22mm setup. Do you use your setup with the UR-E20 touching the knob?