Cumulative brush opacity within one stroke

  • That's a well-known behavior. Setting the Spacing smaller just means you have to tone down the Flow. It has always been thus as far back as I can remember.
    I initially thought that this coupling should have been compensated-for by Photoshop, but when you start to consider the continuum of values between the two settings you showed above, you realize that such compensation is not really possible, and that the Flow setting is the best answer.