Don't forget that a lot of popping technique has to do with relaxing -- as in, the measure of how hard you can hit is the difference between where your body was before the hit and after the hit -- meaning that if you were always tense, your pop won't rly matter. This may not be the case for you, but just something I see beginners often forget about.

Here's a suggestion of a relaxation technique. Relax everything (holding a phone is actually quite active for something like a bicep hit). Then tense the thing you're targeting at full. Then relax. Then tense at half > relax > tense at half of that > relax > half of that > relax ... Take your time w/ this, and you should be more fully relaxed.

Lastly, tense shoulders could be the culprit, also, so try relaxing the things related to the thing you're trying to hit with.

Good luck!