OK this may be a dumb question and I'll look stoopid but I am used to that.

Fin position in waveboards - is the fin position relevant with respect to the rocker, or with respect to the rear stap position?

Reason I ask-
OK fin back = upwind ability and fin forward = looser. Yep that's the most I ever thought about it.
But my new board required me to put the fin back a bit to get some upwind ability, which is great for DTL sailing but not so good for slightly onshore (which I usually sail in) and not so great in the top turn.
Now after a few uses I have moved the back strap forward, as the stance was a bit wide. Likewise, that is good for upwind ability and DTL sailing but may kill off my top turn.

So - if I moved the strap forward can I also move the fin forward and obtain the same feel - or does it need to stay back?

IE: is fin position absolute as it is affected by rocker, or does the fin position relate more to rear strap positioning?

I'm thinking maybe both. With more sailing I'm sure I will find out (if I can sail the same conditions!), but just wondering.....
Maybe a question for the board designers here.....

Think it's more a question for the experimenters Mark.

The other thing to take into account is ventilation, too far back may allow air from the back of the board to attach to the fin. Too far forward and going downwind at speed could also expose the fin to atmosphere.
But rider's weight further forward would counteract this.

Generally further back lengthens the boards water line therefore making it less responsive.