I was supposed to be asleep when I wrote this, so I didn't spend the time to do the math because I wanted to get back to bed.
If a half a 3.0cf bale (or 1.5cf) = 20 gallons of Faux Mix®/Praux Mix®, then 1/3 of a 3.8cf bale is 1.27cf and should produce 17 gallons of Praux Mix®. If you add 2 tablespoons of dolomite lime to each gallon of product made, that would be 34 tablespoons or 2.125 (2 and 1/8) cups. If in fact you did make 17 gallons of mix, and only put in 13 tablespoons of lime, you put in 38% of the amount you should have.