On my FACS Calibur I never get this problem, there is almost an inch
clearance between the sheath tank cap and sensor unit and the filter. Maybe
your instrument has been assembled incorrectly, if still under warrenty I
would complain bitterly until they fix it. Under the drawer on mine there
is about 3/4 of an inch clearance, is your drawer mounted too high?
Simon Monard
Aaron Diamond Center
NYC