The scale uses an even number of slots (8) scaling from 16 to 240 so that there is no “50%” slot. It adds 32 with every slot, 16, 48…
But you are right that having 50% somewhere near to the middle makes sense.
The values of the scales are stored into a configuration which uses the current scale (16…240) as default and when you change it then your individual values are stored with the respective pattern.
If I reduced the scale set to use 7 slots which would have a middle slot then people would loose the 8th slot in every existing setting they already have.
Increasing to 9 seems to be too much slots to me.
But you also said that you have to change the value every time again from 144 to 128.
This is a bug.
What happens is that when you start PM again then it selects the dither pattern you had in your last session, but it does not load the individual slot settings. Instead it uses the default values as mentioned above. If you open the pattern selection window and select the pattern there again then your individual value(s) appear again.
Will fix this.