Only 1 of my whoops would flip after crash with any reliability. Dug around in Betaflight (4.1.2) and found crashrecovery_motor_percent which defaults to 0 by default. From what I understand it that at the default setting it will only use 2 motors. There was a suggestion to use 50%-70% for whoops. I tied it on my US65 by setting crashrecovery_motor_percent = 50% this seemed to really help. As far as I know this can only be set in the CLI so be sure to save it after making the change.
In CLI type
set crashrecovery_motor_percent = 50% save