Decoding C-QUAM as QAM eliminates much of the platform motion with a bump in low frequency distortion caused by intermodulation. There were hacks to the older C-QUAM demodulator chips where you could disable cosine correction and force the chip into QAM mode. In software this should be easy to do, and when the Kiwi folks added CQUAM demodulation, I advised them to add a QAM mode to get around the platform motion issue. I'm not sure that this was done, however.
On HF, ISB would likely be a better choice. You still would have phasing effects, but the complete channel reversal and wobble under fading conditions would go away. I chose C-QUAM initially because of receiver support. At the time, there were no software decoders available for ISB, and to date the only one I'm aware of is onboard the Kiwi.
+-RH