: you used 1/2 inch, Dan C used 1 1/2 divided by 2 so that's 3/4 less
: a saw blade.....heck, one guy even used spray foam built up then
: shaped.

: some use tape to cover the foam some use a wrap or peel ply

: F it, time to roll with something if it's wrong

As you've probably seen from the pics you've found:
Some builders use the foam laid flat on the deck, where the foam sheet thickness determines the clearance between the deck and the coaming (ie the space where your sprayskirt/bungee/knot? has to fit) . Sean used a 3/4" wood riser and then used 2 layers of foam 'on edge' to control the width of the coaming.

Having the coaming 'too tight' to the deck will mean that some sprayskirts will not fit easily, especially if you are wearing gloves/mitts.

Check a few commercial glass boats if you can - most of the ones I've measured have a deck clearance in the 3/4"+ range, widths in the 1 1/8" - 1 1/2" range.

Skirts fit much more securely on round or small 'ocean'-style coamings, so you can get away with narrower coamings on those. If your cockpit has long straight sections at the sides, it's tougher to get a secure fit and still have the skirt loose enough to safely 'pop' with one (the weaker one) hand.

BTW, the pink/purple insulation foam behaves well in the thickness planer, though the 'shavings' get everywhere if you don't have dust collection.