If I ask you this question, how does effective nuclear charge vary as we move down the group?

The correct answer according to the A level cambridge exam will be it DECREASES down the group.

But in nus... it apparently INCREASES down the group because orbitals of higher n values possess penetrating power towards the nuclues and thus not completely screened from the nuclear charge.

I asked my friend to explain to me. In the end... it apparently can increase and decrease down the group. Sigh... which seriously makes no sense. I am seriously bothered by this.