Binding float from Custom Parameter to Window Width, Height

Trying to bind a resolution (float) value from a Custom parameter on a base COMP to my Window COMP Width.
It seems to work (attached) but the moment I try and change the value it snaps to either 1 or zero. (attached circled in pink)

Is it possible your custom parameter has a min/max set? That is visible in the Comp Editor. You can post your network or send to and I’ll check it out.