Hello, I was wondering about why the perspective view on my assembly isnt working. I have cranked it down to as small as possible, but still no joy. This only happens occassionally

The lower image has perspective cranked to 3, but still shows not much difference. This does sometimes occur when there is a sneaky drawing that is much larger than the part, eg, a floor plan, but is not happening in this instance.

Any help would be much appreciated.