I agree with your original idea, if modifications are required.
The Panthera deck height at the front of the cockpit is 29 cm as designed. (BTW, this is higher than Frej by 2cm.)
Raising the deck for foot clearance by less than 3/4" or so (1.5cm) seems hardly worth the trouble. This would be about a 5% increase. If applied to the beam,it would be a difference of over an inch.
So, I'd definitely not opt for the 'photocopier percent enlargement' method, and would raise the deck height only, if required.
Widening a 'surfski'-derived hull seems to me to be missing the point a bit. I'm assuming that you are interested in this boat because you want something fast, to be paddled with a high angle paddle style. Making the boat any wider defeats the whole purpose. Panthera is not a 'tippy' boat IMO withthe designed width, and my paddling skills are definitely not more than 'intermediate'. It feels nothing like my Think EZE surfski, which is a 'stable' (sic) surfski marketed to beginners.

About foot clearance: This can depend on what type of footpegs or footboard you are going to use. If planning a footboard, your toes will be near the mid-line, where the deck is highest. If using 'gas-pedal'-style commercial footpegs at the sides, you may feel the need to raise the deck. You'll need fairly compact footwear when operating the rudder controls in either case, IMO.

BTW, Bjorn mentioned to me during the development of Panthera that cutaway deck sections (flat sections for better paddle clearance fwd and to the side of the cockpit) could be a 'builder option'.

It would only be the work of a day to build a rough stripped section of the few feet in front of the cockpit (2 or 3 stations) once you have the plans. Rip some 'throwaway' strips from 2x4 or scrap lumber, set up a few forms quickly, and build that section of the hull. A few scraps of glass or just a bit of epoxy will make it stable enough for tests. Sit on the floor and stick your feet in there with your usual footwear and see if raising the deck is really required at all.

Thanks John I was fishing for insights like these . A lot of good food for thought right there .
teddy