The Side is always the one that matches with the Shape on the ends, Front and Back are not special, if you hit the Left half of the Front it will do whatever the Left Shape does, same for the Right.
There is only going to be those 3 Types of Recipes, one for the Top of the Anvil, one for the “|” Shaped one (Big Bending) and the third for the “-” Shaped one (Small Bending)