I say this because, before the dynamis update I did it for 3 years and only 2 bst AF has ever dropped.
And since the new changes to Dynamis, been doing it every day and no bst AF has dropped at all.
I've seen so far 4 whm af 2 sch 3 war 2 sam 3 pup 2nin 5 blu 3 rng af drop in Dynamis Windurst since the changes to dynamis.