You are over-thinking this problem!

We use depth-of-field math to computer the span of acceptable focus. We agree on an acceptable diameter for the image disks (circles of confusion). Then we compute the distant point and the near point that will be sharply defined. All well and good but---the moon is quite distant. Objects that are positioned more than 3000 times the focal length are at “infinity focus”. Infinity is Latin for as far as the eye can see. Light rays from objects at an infinite distance arrive at the camera as parallel rays. To image, se set the focus distance to the infinity mark (∞). An exception---foreground objects are to be imaged as well as the moon. Given this scenario, we set the focus distance and aperture per the depth of filed math.

In this case, we set the focus at infinity and the aperture at the “sweet spot” of its aperture range. As a rule of thumb, the sweet spot is about two f-stop below the maximum working diameter.

What I am trying to tell you – Set the camera’s focus at infinity and set the aperture at f/8 or f/5.6.

If we use tiny diameter iris settings such as f/16 or f/22, the focus will likely be slightly compromised. This is due to a phenomenon called diffraction. Diffraction will be heightened when we set the iris to a tiny working diameter, tiny apertures degrade because some of the image forming rays from the lens that are cut off by the blades of the iris (aperture) will nevertheless slither around the opening edges an commingle with the mainstream of the image forming rays. This sets up interference that will degrade the image. Thus, we try to avoid the use of super tiny iris settings. Let me add that most time, the degradation is too slight to be distinguished.