From the beginning of the edge board project in 1970, his idea was to generate as much ''lift' as he could muster out of a 5 foot long glass spoon. So, to that end, the original black and white edge board was built with reverse rocker in the last 6" of the tail.
The idea worked OK, but the board would get sticky turning on bigger waves. His solution was to build up an area around the base of the fin with bondo to give the board more freedom as it transitioned from one rail to the other.
You can see both the reverse rocker and the fin area build-up in the photo.
Eventually, he abandoned the bondo build up and shaped a slight amount of V in the tail of his edge boards, and rounded off the spine so the V wouldn't be dominant.
The reverse rocker idea fell by the wayside as well, after he went to a square tail with a swallow cutout to loosen up the corners. Fabric eventually covered the swallow cutout to prevent cavitation, and obviously that arrangement couldn't generate reverse rocker.