The two middle streams grow your body and shrink your cock. The outer one grows your cock, but only the same amount as the two middle ones shrink. The stats can go higher even after they don’t change your body visually. So you tank points to your body using all the streams and then sync only with the outer stream to grow your cock to max.
In hindsight, the cock can go too much in the negative so it can take way too many outer stream runs to get you cock back. So even if you happen to try only the outer stream, you don’t get any visual feedback. Will change in the next update so you get your cock back faster.