Honestly, abs are really tough. You can do a million workouts targeting all the different ab muscles, but if your body fat percentage isn't in that perfect range, then chances are your six pack won't show because the muscles are hidden. Don't sweat it though, the sweet spot for body fat percentage is really difficult to maintain. It takes a very strict diet and may actually be unhealthy.
In my opinion, you've got a great body and your stomach is trim and fit. Don't worry too much about not seeing the upper abs. Just keep up the hard work and the results will pay off for the muscles you can see
