One of the many mistakes I made when first making LRs, was to have the rear border of the cheek piece too far back which mandated carving that was too vertically oriented, ...in other words, not enough room.
Henceforth, I don't have a hard and fast rule on cheekpiece dims....just make it so it looks good. Usually if the front and rear outlines are "right", it's pleasing to the eye.
Having the bottom edge down too far also was one of my mistakes early on seeing most cheekpieces of originals aren't like that. To get a cheekpiece "right", one has to keep trimming until an uncomfortable feeling hits and then trim some more to achieve a rather small , shallow stock protrusion.
Not an expert by any stretch, but some of my cheekpieces do look OK.....Fred