[Elecraft] Design reasons for X7-X11 case soldering

[Stuart Rohre]

Actually, the desired result of grounding the crystal cans with a direct
lead is a low inductance ground that sets up a shield to crystal signal
blowby, thus improving the performance of the filter.  Stray coupling of the
signal you are trying to filter might be greater if the cans were all at a
higher impedance than direct grounding them creates.
You are converting the cans from acting as plates of a capacitor to acting
as a shield.

Often crystals have a steel type can, and thus you also are getting the
magnetic shield tied well to ground.
-Stuart K5KVH