You really can do it either way, but for a stiff-handled bpw.......
I usually find the exact middle of the stave and draw a line. I grip the bow, placing that line between my pointer and middle finger, and mark where my fore knuckle and pinky knuckle are. That's the handle. Above the handle, I mark out two fingers wide for the arrow to pass, and to see around. Then add the length of the fades.
Once I fiddle this in, the grip is about 1-1.5" below center, but from fade to fade is pretty balanced out. The physical middle of the bow hits the pad at the base of my thumb when drawn, and the arrow is just above that. The fingers on the string are just BARELY higher than exactly in line with the base of the thumb .