personally i dont htink you should do partial squats, if you want to build mass after you do regular full rom squats do something like leg press or hack squats, dont do partials. from experience i know, i used to be one of the put a lot of weight on the bar, new to squatting, didnt go down all the way people a while ago. then i finally with help and advice from others took some weight off (alot actually), used a box with a 20kg rubber plate on top, and went down to that which was just below parrallel to develop my form. my legs have made much better gains since.