I made the GeoCaching lid using the default parameters in the SCAD file, thinking they were the one used to generate the other STL. The default clearance is 0.4mm, which is too much. I might reprint it later, with less clearance, when I figure out what value was used to generate the other STL.
[EDIT] The clearance I was looking for is 0.2mm. New lid is on its way...
It's quite challenging, maybe too much for a GeoCache...