First, rules of thumb are, at best, starting points. I only got my saddle fore/aft fit right after I left the "rules of thumb" alone and used a practical approach.
My fore/aft fitting boils down to . . . put the saddle at the spot where it is easy to go from being fully upright on the saddle to a position with your hands on the hoods. And vice versa. In other words, going to the bars, or sitting up from the bars, is a "neutral" act that requires no hand/arm assistance (and no intentional core strain) at all. It's a neutral movement. And the saddle is far enough back for easy balance with no hands -- hips are enough behind the bottom bracket so that the body balances on that point. (This required me to move my saddle somewhat back from where I had it for decades previously.)
Once I moved my saddle to that position (several years ago), all my knee, hip, back, arm, other issues went away.