I agree with the concept that the outsides of the two polarized end plates do not produce a relative amount gas, as they have no direct opposition current (but do get stray induction currents, and produce minute gas amounts).
The outsides of the end plates, and edge widths (plate thickness edges), are almost irrelative to gas production, and anyone wasting his time calculating the 1 mm wide surface area, of each of these plates, to include it in total surface area, should be in a looney bin.
Those edges, like the two outside surfaces of the end plates, only react with stray currents (not intentionally inducted currents)
The relavant areas lie on every plates surface, that faces another inducted, or pole plate, which includes both sides of every plate, excluding the outer surface of the end plates.
These are set up in +NNN-NNN+NNN-NNN+ array, where only the two outside surfaces of the positive end plates, are turned away from an opposing plate, or neutral plate, and thus all of the plates with the exception of the end plates, are productive on both sides.
The two end plates produce a measurable amount of gas, on their inside (reactionary) surfaces only!
However the question posed, was relative to total plate "area", not total "production area".
Further, with the spacing held to 0.0445 (1.1 mm), production (caused by induction) is increased, as compared to cells with greater spacing.
The amount of voltage induced, is relative to the distance between the electrical conduits (in this case, plates). Further spacing, provides less induced current, and closer spacing provides greater induction (and increased HHO production).
In truth closer spacing yet, would further increase production, but you get very dangerously close to one plate touching another.
It is for that reason, we decided to use spacers, and bolts at each corner, which for the most part, guarantees uniformity of spacing, and less tweaking, or bending of plates.
The plates are punched, rather than drilled, and no matter how sharp your tools are, there is always a slight bit of deformity to the punched metals. Securing all four corners with spacers, is the only true way to secure this minute measurement of water flow between all of the plates facing each other!
Note that Stanley Myers recomended a 0.045" gap (we use 0.0445 gap)