If I recall correctly the rate factors have to do with the fact that your prescription is in an American scale and the FMX uses a metric scale to actual application.  The scaling factor allows the FMX to convert it correctly.  You are doing it correct.  Just punch in what the screen list tells you to.

I've actually had instances where my I decided I wanted to up everything in my prescription by 10% and i adjusted the scaling factor accordingly to make it work.