The answers to a Quora question mainly refer to the factors as generally being, the electrostatic forces of attraction between the electron and the positively charged nucleus and all other events, by which this force is affected, i.e. atomic size (distance of the electron from the nucleus), the penetration effect, the shielding effect (by inner electrons) and the spin-pair repulsion phenomenon.
My textbooks also mention that electrons in the same shell have a "reasonably constant" distance from the nucleus, leading to the key factor of the observed progressive pattern down a period being due to the increase in atomic charge.
I get all that, but what I fail to understand is why none of these sources mention the energy of the electron's resident orbitals. It's my understanding that when an electron is "plucked" from the atom by means of the ionization energy value, or put into orbit by that value, they do so from their orbitals/subshells.
Now, each of these subshells have a different integer value of energy which increases up the count. I also concur that these orbitals have differing forces of attraction acting on them from the nucleus due to distance, inner electrons and the electrons proximity to the nucleus leading to different values of Ionization energy for the electrons "in" them, but I find it difficult to grasp that all electrons in the same shell have similar "distances". In one shell, for instance $n = 3$, there are 3 subshells each of which have a different three dimensional geometry and hence distance from the nucleus. The electrons in these subshells also have different amounts of energy which is what I'm asking about.
Don't these different energy values play a part in their ionization energy? i.e. can't the lower ionization energy of electrons in further subshells be explained by the higher potential energy of that subshell, as the higher the energy the lower the value of ionization energy?
Can't the energy of the orbital an electron resides in, be considered to be a factor of its ionization energy?