Your cycle settings don’t influence the predictions directly; rather they serve as a component for the app calculations.
In addition, Flo takes into account your previous period dates and the symptoms that you enter on a monthly basis. It creates the prediction based on this data.
You can get a quick overview of your previous cycle duration in Menu ( or your avatar) > Graphs & Reports > Cycle Length/Cycle Duration.
However, if your cycle remains stable and matches the duration you’ve specified, then the app will note that and adjust its prediction accordingly.