We embark onto the first microcycle. This prelude is the less linear, more ornamental counterpart to the C Major prelude. It is similarly sructured in half measure harmonic rhythmical pattern. Its development is harmonically driven.
We know that Bach added the sections with tempi markings in a later version of this Prelude. In the original version, Bach ended the piece with measure 25 followed by the few measures of the final Allegro. This brings an important perspective to the proportions of the Prelude. Without the added sections, this Prelude does indeed show a Golden Mean ratio around mm 18-19. The Golden Mean ratio is clearly observed in earlier C Major Prelude. So, in this way also they are related in the microcosmos of the WTC volume.
Now to make a counterargument to creating a complex and uniform tempo relationships throughout the entire prelude... Surely it is odd to see such free Tempi in otherwise rhythmically very strict structure. In my opinion, the Presto-Adagio-Allegro sections must be more proportional to each other than the rest of the Prelude. This frames the section as an extended cadential diversion, but also allows the performer to return original tempo in the final Allegro. However, this choice must not be taken lightly. It is worth noting how the last note is the warm Major third of the tonic, which seems to connect seemlessly into the rest that begins the Fugue.