Datasheet states in the FEATURES section : « Maximum Switching Frequency: 1.3MHz ». However, equations 5, 6 and 9 can yield a switching frequency much higher than 1.3MHz while respecting the minimum off-time of 265ns.

Moreover, Quick Calculator spreadsheet for this part gives a maximum frequency that can go beyond 2MHz depending on input voltage.

What’s the matter with that 1.3MHz maximum frequency?