I think the real answer is in defining what you're doing regarding where your butt is when you need to feel "stronger". I don't race but...when I'm sprinting, sliding up a bit (on the rivet) becomes a stronger position. When I'm climbing, sliding back a bit becomes a stronger position.
If you're riding flat ground and not sprinting, the need to move up on the saddle may indeed be a fit question or problem.
That said...Your fit may be fine as is. Even the pros, who one would assume would have their optimal fit, slide up and back on their perfectly fitted saddles depending on circumstance.