What I'm calling the 'upper edge' is the side of the cover against the pages.
I used the table saw again to take away a chunk of waste wood but finish off with basic woodcarving techniques. I hope you can see how we could have carved it all like this, instead of using the table saw.
In the centre hollow, be careful to leave a little wood at the 'seam' where the pages dive down in the middle - you don't want to break through here!