It's not "my" reasoning. It comes directly from Hayden.
www.haydenauto.com/en/technicians-resources/faq-fan-clutches
www.haydenauto.com
The fan clutch has to match the fan blade. A typical automotive fan doesn't have enough blade pitch (doesn't move enough air) to cause the fan clutch to disengage properly.
So of course the HD or SD clutches move more air--they never disengage when used with typical fans.
Find out what fan clutch is recommended on the vehicle that used your fan blade. Use
that fan clutch, or one like it.