Dave has put it more clearly.
To answer your direct question , I feel it is OK to "level" off more. Again, rotate just enough so one shoulder is just above the surface keeping in mind the other aspects Dave has mentioned especially keeping your lead arm in line with your shoulder.
As far as your discomfort, if you are in fact keeping your lead in line with shoulder and trying to keep it there as you rotate to breathe let's say, and you over rotate, this may be adding unneccessary strain on those areas. Is breathing to the right your 'weak' side?
Check your balance..always.
Tell us more.