The VFD mounting height is adjustable during manufacture - it depends where the sticky pads that hold the glass to the PCB are placed, as the glass itself has pins coming out of one side only. The manufacturers are instructed to seat the display low down, but we have seen variations in production units.

You may be able to help the problem slightly by removing the front plastic and *gently* (and I mean gently) pushing the glass down with a finger on both sides at the top - the position it's supposed to be is around 1.5-2mm clearance between the metal lip below the display and the glass itself as I remember.

Hugo