seeing an example of one of your recipes may help diagnose the issue. 12% capella flavor as a standalone (1 flavor mix) is not bad, but lets say you were mixing a recipe that called for 5 different flavors and you used 12% of each of those flavors would totally destroy the recipe and probably my throat as well lol. Most times steeping does help bring out the flavors in mixes and can also help with the harshness. There's a huge number of things that can affect how your juice turns out such as peppery or bad nicotine, too much flavoring, not enough flavoring, not enough steep time etc. It takes a lot of practice and understanding how your flavors are used alone or together before you start making quality juice. Don't give up, keep lots of notes on the recipes you've tried and maintain those notes with each change you've made and eventually you'll find exactly what you're looking for.