The only mechanism I can see for this 1/10 volume throughput.
The Neutrik design flaw inside the ground/barrel section, whereby tight bush
nut but the 4 sharp tangs have produced pits that then get aluminium oxide
coatings from the chassis metal or tinpest build up at the loose part inside
the barrel section. Say it builds up to 5K ohm resistance , then loss of
ring contact and so instead of say 500 ohm of a pickup it is now 5K5
presented to the input of the amp and attenuated signal current