it looks like that there is quite a lot of user that manage to use a cambo wide RS without this shims... i'd like to read the position of capture integration staff about this !
I'm not one of them
However I use a WRS and a Phase back (actually 2). No shims for the camera, no shims for the back.
Basically, shimming the DB means that the camera unit remains unchanged. Which is good if you use different backs in different mounts (so with different interfaces) on the same camera.
If you can't shim the DB or the camera interface you also can calibrate the lens, i.e. calibrate it to focus exactly at infinity which is technically quite easy but of course it once takes some time to do it accurately. That's what I did.
So possibly my particular lens on my particular camera would not work very well with a DB in a different mount. However for my 2 DBs (both Contax mount) the calibration is fine and accurate. I only use my DBs so I don't care about possible trouble with DBs in another mount.
Over time I had 5 different Phase backs with Contax mount attached on that camera. They were all accurate (with my lens calibration). So the film plane of these backs was probably the same (or at least within the neccessary tolarances). Too - as far as I can tell when focussing objects at relatively close distances - the groundglass matches the film plane (at least close enough to work with).
So is Cambo's calibration off? Unlikely. I was at the factory when they first calibrated my lens and it was just fine on their equipment.
I rather think this is an inherent problem with modular systems requiring such small tolerances.
So... if you use the camera always with the same back (or backs with the same mount) adjusting the lens will do the trick.