Particles, Between Two Curves, can we get a median curve, too? Please!?

It'd be unbelievably helpful to have a third curve, kind of like a weighting curve, between the two curves.

You could call this a median curve, or something like that.

To take it further, it'd be a gradient... but that's excessive. Just a median line would be amazing.

Sorry, I'm not an expect on the fastest maths to weight random values between two extents, but that's probably a factor in this sort of feature.