Or is it that paid F (and presumably F awards) are compensated, but upgraders merely get back their upgrade instruments with no extra compensation? I don't recall, myself. (I guess for paid pax, they could either get the difference in fare or in miles for an award as a refund, with nothing else tossed in, unlike the old days of a CR1 or two tossed in...)

I'm happy to say the only times I've been "downgraded" were when my original flight cancelled for some reason (MX twice and crew once) and the new flight simply didn't have any F seats available. I don't expect downgrade compensation in those cases (though the time they rebooked me onto an earlier flight leaving in like 20 minutes--fortunately I was already on my way to the airport!--I think they could have tossed in some miles as a goodwill gesture).