Ted, I apologize for using engineering geekspeak language.  Sometimes I'm as confused by that language as you so here is link to gps geekspeak to king's english translator. If you scroll down to "Elevation Mask Angle" and read translation then you will know as much as I do about elevation mask angle.

http://www.commlinx.com.au/gps_glossary.htm

I'm not sure if elevation mask angle setting applies to WAAS PRN satellites but it was only setting I could find that might help get low elevation WAAS satellites.  If elevation mask angle is set too low, it sounds like GPS position accuracy could be degraded by low angle 'stuff'.