I think that the calibration size is fine (120mm panel seems appropriate for the object) but the 'problem' seems to be that the scanner is capable of such an amazing depth of field. Here's an uncropped example, rotated for an isometric view, showing a car I was scanning selected in red, which is at the focus point (the car is 370mm long, focus is about 900mm from the camera), and the scanner has also picked up a box I left on the table, and the wall behind that (note the shadow cast by the box). That's a depth of field of about 2.5 metres! So david sees this scan as being 2.5 metres in size, and sets the vertex spacing in the Fusion resolution appropriately, even after I've cropped all of the junk off.
I'll give your suggested settings a try - they look like just the thing for avoiding unwanted 'noise' like that in the first place. Also I guess scanning closer to a wall or other object might help. And not being so untidy of course.