Hi Paul,
I'm not a color expert and I'm not a software coder too. So what I'm saying might not make sense or be wrong.
I imagine a start point from 0 and then a range from -1 to 1. In the pic below (take from Affinity Photo) there is what I have in mind. Starting from 0 I have the ability to increase or decrease the value.
Same thing for bump, normal and every slide that in Octane start from maximum value (1)
Thanx
fabrizio