Think of concave and beveled bottom as two features which should together form a sled-like rails on each side along the concave. And the board sits deeper in the water. Where the outline gets wider and the concave is ending (or starting, it depends
) bottom rail gets wider and creates gradually bigger lifting surface until it joins into one when the concave finishes (this was from tail to nose description
Check the Addvance jet bottom cross section sketch
(somewhere in the middle of the page). Off coarse they don't need to be that pointy, just to get the point.
I would suggest you make the bevel wider than 5 cm. Follow the width you are going for.
Bottom rail also represents a tiping point, and further thowards center it is, greater is the leverage of your heel pressing near the edge. This helps in low wind because if you can not keep the board on the edge, you go downwind.
Making the bevel a bit concaved would make the ride even smoother.
p.s.: Making those hips in the outline (like waterlust graham cracker alaia) again creates just a little wider bottom rails and lift in the back and ads to the playfulness of the board
p.p.s.: You can be more generous with the tail cut
LIke 3- 4 cm in and wide as the concave basically evolving the cut down thowards the bottom rail. It gives better water release on turns, and better control if you need it.
Sorry, nothing on your actual question.
What is your biggest kite?
p.p.p.s.: Nice project's front page!