Hi all, I've had a really quick look at how AMF is effecting my FB.
I fought Alucard twice (who gave an AMF of 0.44) and Inception once (AMF 0.73). For a given level of AMF and FB, the returns are still level, so are still working from effect and not damage done.
My FB was Level: 1,987 Effect: 315.
Returned damage versus Alucard (0.44)
Returned damage versus Inception (0.73)
(My mage didn't last longer than that ;P )
First if we take the melee damage return from an unpenalised effect, it shows that for FB, the first round of ranged combat has a damage penalty of 30%, the second 20% and the third 10%.
As for the AMF return, it looked something like;
(E=Effect, modified by any ranged penalty)
This might not be the correct formula for working out AMF returns against all 4 DD spells, just how it seems to work versus FB.
I hope this helps! ;)