First of all, it should be clear that the annual fee of the patent will increase with the increase of the patent maintenance period, that is to say, the more annual fees will be paid in the future. So if you think the annual fee is different after the change, you should see clearly which year the annual fee was paid.
Secondly, when the number of patentees increases from 1 to 4, it no longer belongs to the category of slowing down patent fees, and the annual fee returns to the official standard.