I had exactly the same problem. In principle, you can also clamp the 75-81 cm version in an 83 cm door frame. However, you then have to unscrew the clamping screws further than Hauck officially "allows". So you do this at your own risk. My assessment: If it is at ground level (i.e. simply separating the access to a room), then this is not a problem. If the door protection is to be used as fall protection when going down stairs, I would personally advise against it.