What about your stats? Height, weight, and bf%
I bet your arms are in proportion to the rest of your body. The best thing I have done for my bis is get really strong at deadlifts, squats, barbell rows, and chins. Along with eating a shit load of food. I know this is a vague answer, but focusing on the above lifts and getting brutally strong at them will cause your bis to grow. Your bis will only grow in proportion to the rest of your body, so focusing on progressing these lifts are key. All bicep/forearm exercise should be secondary to these. To add one inch of upper arm mass you must gain 10-15 pounds of overall body weight.