MAGNET Field Backsight Screen Scale Factor

I switched to optical mode after using GPS mode to set a traverse network for a drainage study of a conservation area. I've just started using this software, so please bear with me. I'm somewhat familiar with grid vs. ground distance and scale factors. Anyway, the backsight screen had a scale factor of < 0 selected. I assume GPS mode created that scale factor based on type of projection, etc. being used. Is that correct? I also assume, that I should keep using that same scale factor when using optical mode. The fact that central Florida, with some exceptions, doesn't have any large changes in elevation makes considering a scale factor irrelevant. That has been my experience. I will dare to say, that use of a scale factor is dictated by the type of survey being performed. Opinions anyone?