How to configure Post-Processing Stack v2 volume blending properly

I'm trying to figure out how to correctly set the values in custom post processing stack effects so that they behave in similar manner as the built-in effects. When I try to test this by adjusting "Weight" parameter in Post Process Volume, it looks like my effect parameter values jump to 1.0 (or some max value) and start fading down from there when dragging the weight slider to left.

I read the writing custom effects page again (https://github.com/Unity-Technologies/PostProcessing/wiki/Writing-Custom-Effects) and there it says this:
"For parameters themselves you can use any type you need, but if you want these to be overridable and blendable in volumes you'll have to use boxed fields. In our case we'll simply add a FloatParameter with a fixed range going from 0 to 1. You can get a full list of builtin parameter classes by browsing through the ParameterOverride.cs source file in /PostProcessing/Runtime/, or you can create your own quite easily by following the way it's done in that same source file."

Now I'm just checking the source code of the built-in effect but so far it hasn't dawned to me what should be done. I hope there's some way the values can be set to be ignored. I'd imagine this is obvious but I just can't see it right now...