Invert EFX Curves

I would like to have an option that i can invert an EFX-Curve, so that the curve starts and goes below the 0-line first. Instead of going above the 0-line.
At the moment the only effect which does this is the ramp.
With that option it would be possible to only lower values with effects (Length set to 200% for the effect), at the moment we only can add values when we apply these settings.
Offsetting doesnt help. As the curve then also starts with going above 0 but just with a phase-shift.