Highest SHGC sliding door in Canada is 0.63. Why not higher? – GreenBuildingAdvisor

NRCan’s downloadable data for all sliding glass doors has 21400 rows, apparently one row per door option.  The highest SHGC is 0.63. Only 4 doors are higher than 0.6.

Why are there no sliding doors with an SHGC higher than 0.63?

Does the frame of each individual door reduce the SHGC?

Does the frame surrounding the complete set of doors reduce the SHGC?

Those two frames mostly overlap so shouldn’t be double-counted.

For a door 36″ x 84″, a 2″ frame all around would reduce the area like so:

(32 x 80) / (36 x 84) = 85%. With a 3″ frame, it’s 81%.

If the frame affects the SHGC, then the theoretical maximum seems to be around 83%, so why is the maximum made 63%?