Do you not think the cartridge designer and manufacturer knows what they are doing when they recommend a minimum of 100ohms ?
If I had to guess that spec is set to assure near maximum output of the cartridge. Changing the loading value makes subtle but easily audible changes for many. I know of several people who routinely load MC carts at 3-5X the internal impedance. They do this out of sonic preference and not out of ignorance or to thumb their noses at "accepted practice". I have yet to see a published minimum load that comes anywhere near the <3Ω of the MCCI which precludes their use in general if one were to adhere to the manufacturer's suggestion.
but for those who are more open minded
Odd... it seems to me that insisting one trust a published suggested load over their ears is just the opposite of open minded.
I am not saying that the OP is correct in their 20Ω choice or exactly why that value was chosen. It may very well be that the 4dB reduction in cartridge output from that cartridge-load ratio may be partially responsible for some additional noise. The point I was / am trying to make is the disconnect between minimum recommended load and the use of a stage such as the MCCI.
dave