Hosts such as REAPER normalise the program parameter value by dividing
the program value by the step count, rather than going via the
parameter's toNormalized function. To be compatible, we should use the
same scaling technique. At time of writing, the coversion process is
detailed under the heading "Conversion of normalized values" on this
page:
https://developer.steinberg.help/display/VST/Parameters+and+Automation