I get 8 sq.ft. with about the same resistance as a 2x2 single pain window.
Much ado about nothing...
Not exactly clear what your measurements refer to, but if I had a 2X2 single pane in your climate, I'd change it out. I also know that having your slab floor extend outside like a giant cooling fin is going to get you a bigger heating bill.
Is that a tremendously small garage? That sort of construction for a 22 X 22 garage usually yields at least 10K-12K BTU load for a 50F delta so maybe you are doing something special with 20' of fin which gets you what.....7K or 8K at that temperature?