Might want to take a flashlight and look down into the fin box on the rear taper.
Sometimes the factory fin box tolerance gets a bit large and they have been
know to stick a blob of black epoxy in the rear taper to shim up the original fin
to the correct level before they ship the board.
Pretty sure they do it very much like the 2nd option I suggested.
Take a look and if you see a lump of epoxy about 1" down on the rear taper
radius in the fin box, that was the factory's way to fix an oversize fin box.
I've seen a few where the lump of epoxy broke off and the fin now drops too
far into the fin box.
Before you apply the epoxy to the fin root.... or to the taper in the back of the
fin box, try to wipe it a bit with a paper towel with a little acetone in it.
Just be sure not to spill any acetone on the board or in the fin fox as it will
really make a mess..... an clean and prepped for exopy application mess.
The acetone will prep the fin root or fin box so the new epoxy you apply will
Also, remember, the fin bolts are only there to pull the tapers into engagement
and ensure that they stay engaged while you sail the board.
They add nothing to the structure of the fin or the fin box, so cranking the screws
down real tight normally causes more problems that it fixes
That is usually what dislodges the Cobra applied lump of epoxy shim..