OK, so you know the deal - you've just touched down, light as a feather from a jump where for one blissful moment the surface of the water was just some distant memory and your mate says 'Yeah - 15ft I reckon!'
Now I know it 'seems higher' from up there as he's looking at the bottom of your board and your eyes are 5-6ft higher up than that - BUT - and I've only just thought of this - surely you should then add that 5-6ft back on - to account for HIS eyes being 5-6ft above the sand/water!
Yeah... 20ft.... Whoohoo!!!