a VM does generally stop production ( pending efficiency % varies ) which is one off their strengths, - Yes I agree, however when the boiler vapour temp is 80C, ie wash has alcohol in it, there is no reason for product rate to stop or take off.
Could your column be flooding - liquid climbs to VM branch then syphon down condenser increasing flow ??
I doubt it- have spent some time and over 40 runs per year varying power levels etc.
How tight is the packing. ? Last year I removed all the ss packing as it was compacted and holding pressure in the boiler. (not good) . I removed half the packing and found that efficiency was slightly reduced.
During the last run I can obtain 95% @ 20C at 300-330 mL per hour.
Back to your initial comment regarding the horizontal length ie 3x the column diameter, ie 6 inches or 150mm. Mine is 4.5x ie 9 inches.