Green Xenon wrote:
"But wouldn`t multipath intrference be as much of an issue in FM as in
AM?"

Ionospheric multipath mucks up both FM and AM because the sidebands have
both phase and amplitude altered almost randomly in transmission.
However, FM is less sensitive to amplitude variations and reduces the
apparent fading. But, a better way to reduce effects of fading is by
diversity reception which automatically switches to the best available
signal given several options which are from different carrier
frequencies, antenna locations, or antenna polarizations.

Best regards, Richard Harrison, KB5WZI