190lbs. @ 17.6% = 33.4 lbs. fat- you are around 157 lbs. LBM (lean body mass)
189lbs. @ 15.9% = 30 lbs. fat- here you are around 159 lbs. LBM.
You want to figure your protein, carbs and fats based on your LBM. It appears you are actually losing fat and gaining muscle. You are obviously doing something right.
You don't mention what your weight-training regimen consists of, or when you are doing your cardio. As long as you continue to gain muscle and lose fat, or lose fat and maintain muscle, you will be fine. To actually gain muscle and lose fat as a natty is commendable.
How low you can get as a natty is entirely relative unto you and another man your size with similar genetics. To "not look like a swimmer" requires you to have a good solid base of muscle proportioned in all of the right places to begin with.
A natty can get a six pack, no problema, but whether or not he's gonna look like a fashion model is another story. You may end up having to go through a process.
First: Get that bodyfat down into the single digits, or at least to 10%. You may not like what you see.
Second: Build up your muscle slowly (where needed) and keep those bodyfat levels "in check"
Making lean solid gains is probably the best method for a natty. You may have to cut the cardio a bit, but for now, it seems to be working.
If you were to post pics of yourself in a relaxed pose, it would be a lot easier to help you with your goals. My guess (without pics) is that you will probably need to cap your side delts, build the outer sweep of your quads, grow some calves, build some arms, widen the back...
I'm kinda being facetious here. This is what we all want and need.