How ridiculous. Haven’t you heard the lower the alcohol the better? 
Could it be the glu/fru ratios?
Do you guys check that at all?
I have found in the past the more ripe a lot comes in the higher the ratio tends to be all else being equal for PN.
Though I usually just assume there is more of a soak up that cant always be accurately measured early on.
I have also found open top ferments have a lower rate than closed top.
Some ETOH (and other volatiles) blow off over the 3 week ferment with peak temps in the low 90’s.
I have read some older texts from the 60’s that state normal conversion rates of .50 which would be nice, 24 brix and 12%. 
In my whites I have seen as high as .69 and average .65.