In this case, i.e. if the park rates are fixed and don’t change, both methods will result in the same payout.

Let’s instead assume the current park rate for 3 months is 2.5%, and after 1 month shareholders suddenly decide to raise it to 5% (i know this cannot be in one block, but for the example its fine) and after another month they suddenly decrease it again to 2.5%. So everyone who parked in the right window, will get 5% as payout, will everyone who started to park outside the window will get 2.5%, correct?

In my proposed method all people who parked before the latest decrease (2 months in the example) and at most 3 months before the increase, will get 5% and all who came later will get 2.5%.