I think you're referring to
this (1K0129627B), right? (Part number is for PD100 BEW, may be different for yours.) I think it's around 70mm on the intake side and 55 on the turbo side.
I had to replace mine because someone put a hose clamp (worm gear drive) on the turbo side and it ripped through. That reminds me, I need to order some of those remote cable-operated hose clamp pliers (for spring clamps) so I'll be able to install/remove the factory spring clamp there. When I reinstalled it, I put the worm gear clamp back on, but didn't tighten the clamp as much, to avoid ripping my new part.
It has slipped off ~1cm or so, but would have to move at least 2cm more to come off the turbo, and takes a good deal of force to move, so I'm not too worried. Are you running big boost? You wouldn't expect that to affect the
intake side of the turbo, but I found
another thread where the speculation was that when you let off the throttle and the vanes open, it may dump some pressure back into the intake.
Also, make sure the plastic intake pipe upstream of this is properly fastened. I think there's one bolt on top and on the side of the engine...