Testing Tempest with UIFX64 .175 all parameters are active with/without HLSL enabled. Changes in-game may not register until the TAB menu is exited and the game un-paused.
Line width prominence is determined by width minimum, maximum, and intensity. A measurable effect starts with minimum being above 0 (the stock .75 seems a good value) and maximum being at least .5 above that - else no change, right? The stock settings of .75, 4, and .75 look great here - though maximum at 2 is about the same. The ugliness comes from flicker. I don't know where that came from, as I did not see that in the wild. Some people like it. I think it's awful.