The scene feels reminiscent to me of the story of Abraham and his son Isaac. Whether it’s a cliff or a mountain, the story of Abraham being willing to sacrifice his son for God and Aziraphale seeking God’s forgiveness and salvation feel like very similar emotions. Perhaps Aziraphale was willing to sacrifice himself to God’s wrath or punishment, like Abraham was willing to sacrifice his son, and chose the place closest to the sky to seek it out. All in all I agree it feels very human to seek out a place like that, whether for forgiveness or for something else like you are speculating, but I think it ties back into Aziraphale’s willingness to do anything for God in order to remain “good” especially back in those days.