All that said, I have found that there are some liquids that simply don't wick well in a Protank no matter what you do. Even with a great rebuild and cotton, I have a 50/50 dark coffee juice that just burns every time after the first three hits in a Protank. If it's your juice that's the issue, it's time to move to a rebuildable dripping atomizer and save the thinner juices for your Protanks.
^^^^this. OP I think the type of juice you're using is what's giving you problems. I agree that if you want to continue to use that type juice you should consider learning about RDA/RBAs so you can manage the coils yourself.