I have mine set as dedicated (factory equipped projector truck's have this already wired and is what is used as the drl circuits) and I'm fairly certain that when I go from auto to parking lights while drl's are active they'd switch to parking. Because they use the same lights, although different circuits they might visually look the same. Lowering the voltage should dim the parking lights enough to give you what you are looking for.
2018 2500 6.4L Hemi Tradesman
1990 5.9L 12v Cummins W250
While I haven't tried lowering the voltage I can tell that the parking lights are being overruled by the DRL's. As soon as I disable the DRLs on the 8.4 the parking lights go to the normal parking light intensity, which is the same as with the headlights. I don't want them dimmer than this.
So if it's dark enough for headlights and I am in Auto I have normal parking/headlight. I then switch to off and DRL's come on full. Then to parking and I get my cab clearance lights, tail lights, and full DRL brightness on parking. Then to headlight I get my DRL's to dropout and parking lights come on.
So in the end I am thinking that adjusting parking light voltage will only lower the parking light with headlamps on, since I don't think it's using that voltage in parking light mode.