the problem related to the frame duration is, that different waveforms apply different filters in time domain. However, the whole simulator processes data on a frame-basis. Therefore, if different waveforms are applied in different cells, they still have to be similar across cells such that the frame processing is still possible.
I am sorry for my late reply. I will look into this issue. Are you using a single waveform, that is, FBCM, in all cells?