From my understanding, you do not need to worry how high above sea level you are when dealing with an artificial horizon. There’s no DIP correction to take into account when using one because your horizon is essentially directly in front of you instead of miles away and you’re looking essentially into a mirror and not a horizon. Aside from remembering to divide your Hs by two because your horizon is a reflection, the only thing to keep in mind is the altitude correction for the celestial body you are considering. If you are shooting the sun or moon, for example, you have a choice to overlap the celestial image with the reflection, which erases the semidiameter correction (exactly like taking a star sight), or stack them on top of each other, which mimics an upper/lower limb sighting, in which case, you would take all celestial body corrections into account. Hope that makes sense!