Rpen is correct.

Saddle set back is a function of leg length and determining the proper place to have your saddle in relation to the Bottom Bracket. It has nothing to do with reach or balance.

Figure out where you saddle needs to be first.

Then, if you need to adjust reach, you change stem length.

As for the video of a guy on a trainer leaning forward with his hands around his back, that is only a reflection of his core strength. It has nothing to do with the quality of his fit.