[sd79812]

If effective nuclear charge is net pull inwards by all the protons in the nucleus on outer electrons, why does removing a outer electron increase the net pull by the protons on outer electrons inwards? As far as I know, Valence shell electrons don't shield other valence shell electrons from the proton in the nucleus, and outer shell electrons don't shield inner shell electrons.

I'm learning about cations smaller than their neutral atoms.

If F_electrostatic=kq_1q_2/r^2. Let q_1 be charge of nucleus' proton(s) which is constant if you make a neutral atom a cation. AFAIK: If q_2 is negative and becomes smaller because you pulled out an electron to form some cation, then you're decreasing attractive force inwards towards the nucleus, which means that quite absurdly you're decreasing effective nuclear charge contrary to what my source says.

[Corribus]

As far as I know, Valence shell electrons don't shield other valence shell electrons from the proton in the nucleus, and outer shell electrons don't shield inner shell electrons.

This is incorrect. Valence shell electrons do shield other valence shell electrons; the effect is not as strong as the shielding effect by inner shell electrons, but it is not negligible. An outer shell electron may even spend some of its time closer to the nucleus than an inner shell electron, meaning a valence shell electron may exhibit a small shielding effect on an inner shell electron. Depending on your level of study, you may want to review structural models of the atom to have a better understanding of why this is the case.