This is strange, the readout modes for flats, darks, and biases are controlled by the ROModeInfo config file. My info on using #romode in the ImageSet for the scheduler applies only to data/light frames. Cal frames and flats are run by ACP under Scheduler's control at the appointed time(s). Here is now to control readout mode with ACP observing plans (which are used for Scheduler cal frames) and ACP flat fielding: