Furusato nozei year n+1 question

Hi all. I have read the wiki page on Furusato Nozei, but the following was not extremely clear to me (it was somewhat clear).

Lets say that my income in year 1 was 1000万, and my income in year 2 was 500万. I will start paying the local taxes on the year 1 income in June of year 2, and I will start paying the local taxes on the year 2 income in June of year 3.

So, what I'm wondering is, is my limit for Furusato purchases made during year 1 based upon my 1000万 of income in year 1, and my limit for Furusato purchases in year 2 based on my 500万 of income in year 2?

The reason that this is a bit confusing to me is that if I have saved up money during year 1 that helps me make additional Furusato purchases in year 2, I have to estimate my lower income and limit during year 2, and make fewer Furusato purchases during year 2 than year 1. Also, during year 2 I am paying relatively high local taxes, but I still have to keep in mind that I have a lower limit in year 2.

This seems correct to me but for some reason it's still counterintuitive.