My Phil3 are now in the family room. The back is 6 inches from the wall.
I think the sound is slightly affected. So I stuffed 100%. Now they sound perfect again.
When they were in my HT room, they were about 18" from the bass cab back to wall. I didn't notice any difference with the stuffing.
So I think if you are way out from the wall like GranteedEV, 0% fill would be great. If only inches out from wall like me, 100% stuffing is right.