What are you using as a still? Reflux is supposed to be the best, but you have to tune the heat and return. As stated, there is a lot of info available to make shine, but most shine gets watered back down to 40% alcohol from the 80-95% pure distilled.

I would think 10-20% means either your yeast isn't producing like it should or your not allowing it eat as much sugar as it could. 10-20% means your only making 1-2 gallons of alcohol per 10 gallons of mash, I would think the yeast could do better.

You may also want to try this http://www.amazingstill.com/ to pre distill your mash.