The item levels of scepters and books seem to imply that more precious metals conduct aether better. Is there a reason to assume that does not hold specifically when facing Voidsent? Better aetherial manipulation means stronger magick, and wards are magickal in nature, are they not? At first glance, I'd assume it still goes Copper > Iron > Silver > Mythril > Electrum > Gold > Rose Gold > Platinum.

Hopefully whoever started passing around this information has a citation, because I can't recall such a thing

DISCLAIMER:
The following is mostly in jest.

There's this an item called a Gold Needle (for curing petrification) and the item description is that it's made of pure gold. The materials? Electrum, spoken blood, and ahriman wings. If Electrum is a silver/gold alloy, how do people blood and voidsent parts leech the silver out and leave you with a pure gold needle!? Perhaps this is related to your phenomenon!