your biceps will be smaller than you like for one or two simple reasons........
1. the amount of weight you lift
2. and how much of that weight is transfered onto your muscles.
you simply need to get stronger, often performing less working sets a week is a good idea. make sure you only perform a few working sets for biceps per week, and try to hit them maybe twice a weeks, but only for low volume. using a rep range of around 8-15 so that your form is good and the weights are being transfered to the muscle to stimulate growth.
i recommend trying drag curls instead of regular barbell curls as they allow the weight to be moved by the biceps without your body english taking the brunt of the weight.
also i recommend using indirect training to give your biceps more frequent stimulation. so do undergrip chins on back day along with reverse grip rows etc.
basically whatever you do if your not taking the weight on your biceps and your not progressing in sets and reps on the basic bicep exercises each week your not going to improve. progressive overload is king, but make sure your overload with high intense sets not lots of volume!
I watched the mike mentzer video about HIT. You should try a variation of it, because mentzer likes to avoid momentum, overtraining, and partial reps. It's an insane workout, but it absolutely can build some huge guns.