Back to FWH.
I have to say that earlier hops additions gives me harsher and lingering bitterness.
Not sure why FWH would not do the same.
This is my experience.
Kind of learned it hard way with 350 gallons of beer.
In George Fix's book, principles of brewing science, he sites the blind taste tests where FWH was show to have a cleaner, less harsh bitter taste, despite having higher measured IBU's. I think Gordon goes into this in his book too, and he is a big believer in FWH. I only tried it once with an APA. I took a medal at a fairly large competition (300+ entries), and my scoresheets described the beer as malty and dry with a bright hop flavor and no harsh bitterness. I am fairly convinced that FWH does produce different flavors than 60 minute additions. I know Jamil is not sold on it tho.
I know that regardless of traditional or FWH,when I use a low alpha hop to get a lot of IBU's, then I get a lot of vegetal material (polyphenols) dissolved in the beer and it comes out grassy and astringent. To me, that makes the bitterness harsh.