Assuming azeotropic behavior you likely cannot typically seperate those two cannabinoids via fractional vacuum distillation. Simple distillation is called for under vacuum. Frankly fractional distillation under deep vacuum conditions is contraindicated even though attempted frequently from what I can see. Fractionating devices in this situation create a slew of problems and it is unusual to shoot for deep vacuum but then go on to install fractionating devices if you have had experience trying this before.
If you can pull a very deep vacuum then your temperature is your fractionating device although once again using a distillaton column of any kind hobbles seperation attempts owing to the enormous relative amount of energy you must pump into the compound simply to transfer the heat up into the column and attempt refluxing the thing to achieve fractionating. In fact if you can pull down to mean free path flow (MFP) conditions of say under ten or twenty microns then the nature of MFP flow nearly precludes the use of fractioning devices without some means to actually bypass the device and usually at the expense of adding heat into the process.
In MFP conditions molecules can no longer be herded up and around fractioning devices or corners - straight lines only as a rule. Vacuum distillation at all is generally not the kind of task a seperation expert is going to attempt to employ fractionating devices with and outside of this industry I see no references to widespread use of fractioning columns in vacuum distillations. Witness the super high bypass mode distillation rigs now being seen where the design calls for complete bypass of the column itself of lighter fractions being pulled up simultaneously with the heavy fractions and quasi-seperation is accomplished by blowing the terps past the collection vessel. Messy and perhaps needed for production but an inelegant solution to say the least. The cost associated with doing this is enormous comparatively.
The fractionating possible via an evaporative process will rely on strict temp control. I measure the boil routinely at 127°C nominal and at 3/4 of one micron indicated as measured on the glass between the boiling flask and heat mantle (for temp). This is an order of magnitude lower than can be accomplished in a verticle distillation rig owing to the need for the thermal carrier to be the oil itself which then introduces unknowable periods of reflux. The best system imo for such a delicate seperation therefor is one in which reflux is avoided altogether. I have posted many videos of how I go about refining THC into very high purity. This can only be accomplished by keeping fractional equipment out of the way and thus enable very deep vacuum levels that represent MFP flow condtitions. Remember, in MFP flow conditions a fractionating device is a barrier and cannot provide the kind of delicate fractioning you seek without significant mods. We often see in literature the term “molecular distillation”. From what I can tell the term “molecular fractional distillation” is not normally envisioned outside of this young and learning industry. Residence times get brutal and it is not the right tool for the job at all.
A horizontal or other single theoretical plate distillation with tight temperature control is the best shot at separating such closely related high boiling point oils. I personally have switched most of my operations to just a cryogenic sublimation apparatus operations modified for short path MFP molecular distillation. The collection point is one inch above the puddle and the unit is easily converted to a true single plate distillation rig. However a deviation of just 20-30°C above the target temp very easily causes fractions to overlap. In a vertical rig you simply have to carry this much extra heat from bottom of boiling flask compared to just the top of it really just to pump the needed heat into the top of the column. This is the achilles heal of vertical distillation columns.
The solution is to skip the notion that simple vacuum distillation be carried out as a fractional vacuum distillation and instead target a more controlled temperature solution like a simple horizontal configuration. The upside is the unit is super simple to set up and run as a horizontal rig and then the fractioning done is controlled by heat and stir bar energy alone and not relying on carrying excess heat up into a column which also carries along with it contamination of your twrget compound.