Just to humor Greg, somewhat, I made a quick mod. to the system.
I was thinking about a "little help" on the cold air return. ... box, fan, couple to pipe.
I had an old humidifier sitting in the basement, being used as a "catch all" shelf, so to speak. I cleaned it up a little, added a duct take off with some aluminum duct tape to the back, over the intake, attached it via flex duct to the cold air return pipe, plugged it in and I was up and running in 15 minutes. (The humidifier acted as the "box and the fan", plus allowing easy adaption of the duct take off and 6" flex duct.)
Initially the temperature at the cold air return decreased, probably pulling cold air from far, far away. After 45 minutes, the mid room temperature has gained 1* from 74* to 75* (outside is at 39*) . It's pretty obvious that I now have a whole new situation to fine tune.
It may not be beautiful, but it was pretty easy to use as a test.