Blend amount using expression pedal

When using an expression pedal to blend between two amps say, maybe have the ability to adjust at what amount of travel on the pedal the percentage of blend will occur. Like a taper amount? I know theres a minimum and maximum amount, but its just not quite what it could be.

I blend between a clean and distorted amp using the splitter feature. But at say 20 percent travel, going from clean amp to distorted, its like a switch instead and not enough of a taper to roll into a smoother transition.

I control multiple values to try simulate what i want but theres not enough control as to how i want them to taper.

I hope this is clear, i dont think i can explain it any better?