Where are you getting this info?
Yeah, what he says corroborates with what JY is saying. 3.5 = edge between bevels 3 and 4. Now, I'm sure he adjusts the grip against surface, and so he may have a more true SW grip on clay. But it's basically closer to Eastern grip than SW. It's counterintuitive, but again JY has the analysis and video footage to back up what he's saying.
Fed's FH swing is really weird; it's got classic and modern elements mixed in a way that is counterintuitive. Like, for example, he closes the face with that Eastern grip, so that he has lively wrist action when the swing goes forward.
There's really good reasons why the rest of the field simply cannot replicate the shots Fed can do. Fed's FH is not merely the most advanced FH in the game. It's literally an evolutionary step forward in the way Borg's FH was in his day. But there's also good reasons why 99% of other people shouldn't try what he does. And there it makes more sense to use a SW grip as what Hewittfan is saying.