@ExTek90 had a method of true fractional extraction where he would run a light fraction first pulling off terpenes. Following this would be a quick heavy fraction run pulling off waxes, and finally the last heavy fraction would pull the remaining acidic cannabinoids. Although, if you read further and continue his procedure, the ultimate goal was to produce crystallized THCa, I do not see how this would not work for what you are trying to do.
Your calculated densities seem sound, although, I don’t know if there is any info out there that would elicit parameters geared towards fractionating CBD off from the rest of the THC and other cannabinoids. Might be out of the hands of CO2 extraction and more applicable for fractional distillation or chromatography.