Ken,
The board will go down, because there is nothing to stop it from going down. The wing wants to go down also, but it isn't large enough to create enough force to bring the ski tail down. I believe, due to the size of the wing, compared to the lenght of your ski. A wing is about 1 inch or so long, while skis are around 67 inches long. The length of the ski, gives it leverage on the wing, and it is too strong to allow the small wing to pull it down. Now, if you put a large enough wing on the fin it would bring the tail down. I don't believe you could actually ski on it though. When you were holding the board behind the boat, it wanted to pull you off the platform. So you can see that it is creating drag. The drag on the ski plus the pull on your body from the boat forces the nose of the ski down. Just my thoughts.