Never heard that about becoming more like the moon.
In fact, everything ive ever read and heard from astrologer friends Ive known is that if we are actualizing our beings we grow more into our sun signs.
And if anything, the moon energies fade as they are more residual habits of past whereas the Sun symbolizes the central equilibrium energy where our astrological energies gravitate around and are fueled & colored by. Even the moons gravitation and presence exist due to the Sun.
The more we grow into our sun energy the more we are fulfilling our core, central astrological energy. At least from what ive heard, read and intuitively feel makes most sense.

Although Ive also heard there is something to growing into the ascendent sign as well, but still less so than the solar / sun signs energy.

Ultimately, the most important aspect is what we choose to focus on, feed and believe, I believe. And our choices & attitude ( which can transcend astrological definitions ) will color and influence whatever other energies or qualities we otherwise have as well.

Example - the qualities Christina attributed to Scorpio "Now I usually irritated, sarcastic (-er), suspicious, and more to myself" can easily be seen in people of any other sun sign as well depending on how they are expressing themselves. Its just mind use, regardless of the elemental energetics that can more accurately describe astrological signs.
Perhaps this is a distinction made less by pop astrological texts & astrologers, but discerned more by those viewing astrological signs more in terms of elemental qualities & energies rather than strictly defined psychological or behavioral traits.?

As in cardinal, fixed & mutable / water, earth, air & fire. Which in themselves are just energies, neutral in a way in terms of how use of such energies, mind and behaviors.
Kind of like chinese medicine views elements ( although a different elemental system having five rather than four, primary elements ) as innately neutral qualities, experiences or expressions of the ultimate source energy. Whereas sarcastic, suspicious, irritated, more to oneself is still just as readily human & gemini ( or any other signs ) energy simply redirected to be sarcastic, suspicious, irritated, more to oneself.?