My first head and face carving was done on the corner. Most of what I read stated that this was the best way to start out. Also at about that time some one told I wouldn't be satisfied with the faces I carve until I'd done at least 1000 of them. I never kept count, but I started out on the corner and kept it up for a long time. But soon I discovered that if you want to expand your carving to full bodies, you had to learn carve a face on the "flat" of the wood blank. I resisted, but soon found out that my corner carved figures were all "pigeon-toed" and weird looking. My first faces carved on the "flat" had small noses and were truly square blockheads (Above Elf).
I have noticed that beginners that start carving faces/heads on the "flat", end up with a squared block head. If you are carving a face on the flat, be sure to remove enough wood to shape the face, and the back on the head. You must establish "corner planes" that allow for the nose to exist as the furthermost part of the face. And remove wood to achieve a realistic roundness to the carving.