I do it different ways depending the the type of bow. With regular selfbows, backed bows, trilams, sinew backed bows and other natural material bows, I usually build up a very minimalistic shelf with leather. When I'm shooting, it looks like I'm shooting off of my knuckle. Sometimes I make selfbows that I DO shoot off the knuckle. Depends.
When I make glass/wood laminated longbows and recurves, I cut a narrow shelf into the riser. Some cut closer to center than others.
They all shoot fine for me.