I have a Canon 400d ( rebel XTi ) and a Sigma 10-20mm lens, I cant mount the lens on the top arm at the spacing recommended i.e between 93 and 99 depending on focal length. because the lip for the lens hits the Nodal Ninja arm and the lens ring (to change the focal length) also presses against the side of the arm

please see the photo attached to explain

Any suggestions on what I need to do to get round this problem ?

Thanks for any help offered