Yes, you should also set TURBO to 175 if you want step-down to work.
Also, if you want the modes to remain evenly-spaced, I suggest running the bin/level_calc.py tool to calculate a whole new set of PWM levels. If you don’t use 255 though, you may need to edit level_calc.py to either set the value there or uncomment the line which asks you for that. Here’s what it does after I uncomment that line and re-run it with a max of PWM=175 for a 960-lm turbo:
> ./bin/level_calc.py 4 1 10 175 960 y 20 10 140
1: visually 2.15 (10.00 lm): 0.00/255, 20.00/255
2: visually 4.72 (105.46 lm): 0.00/255, 192.56/255
3: visually 7.29 (388.17 lm): 64.68/255, 255.00/255
4: visually 9.86 (960.00 lm): 175.00/255, 0.00/255
PWM1/FET values: 0,0,65,175
PWM2/7135 values: 20,193,255,0
I got 960 by estimating an actual maximum of 1400 lm, then multiplying that by 175/255.
If turbo isn’t 255 you could also try making turbo a little more efficient by putting some of the load on the 7135 chip. On a XP-L or XM-L2 it’ll generally get about 140 lm on the 7135 alone or 1400 lm on the FET alone… so subtract 140 lm from the FET value and set the 7135 at full. In this case, it would mean the brightest mode is 150 on the FET and 255 on the 7135. But that’s totally optional; it’ll make turbo more efficient, make the PWM harder to see, and make its tint slightly warmer.