I don't see that as a crippler.
The rationale for a receptacle at deck height is the need -- triggered by the functionality of the space for everything from festive lighting to BBQs.
At 4x5 feet, 20 square feet is going to provide a GFCI receptacle for anything larger than a landing.
11.999 square feet will always be rounded off -- to 20 sq ft.
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GFCI receptacles have gotten so cheap - and their safety value so apparent - that the Code is placing them all over the place.
Trying to design them out ( value engineering ) is a total waste of effort, in my opinion.
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In my commercial installation experience -- we don't even attempt to chain GFCI receptacles -- the end user would never be able to figure out where to re-set the tripped device.
