I've sailed previous Exocet Cross versions, but not the latest. Its good to read reviews, especially if they give the good points and the bad points. Too many 'user reviews' seem to ignore any bad points.
The earlier Cross boards are good for gybing but you cant gybe them in a tight turn like a FSW as they dont have tail rocker. A slightly wider arc is required.
I'm wondering if the reason you dont get enough lift from the 36cm fin as you have the mastfoot too far forward.
I put the mastfoot at around 130cm, which is very near the back. Ignore the marked settings as they always seem to be wrong, get the tape measure out. What distance from the tail does the mast track start? I use Ezzy sails and am lighter than you at 80kg, so its not necessarily the same setting as you would use.
I've never had a problem with Exocet's straps twisting. Do you have the metal tab under the screw? I dont use the anti twist tabs, the dealer said they sometimes break. You have to tighten them hard with a screwdriver though. Pozi 3 iirc.