To give you a little more perspective on the sizes I'm talking about when I say "roughly 6 inches", I'm talking about on the screen monitor, not on the landscape. Also, obviously there are ranges to all this, but the point I'm trying to make is that the range is not one of many orders of magnitude, but all within the same order of magnitude. Here's what it would mean in the case of Skullface's head from MOC AB1-08403.
In this case, the scaled pixel width is 4.56m/pixel. The width of the swath is 1024 pixels or 4.67km. Skully's head is in the middle third of the swath, covering an area about 250 pixels x 300 pixels, or 1140 meters x 1368 meters.
Viewed at 100% (actual size) in PaintShop that's roughly 3 inches by 3.5 inches.
Like I said, there's a fairly broad range within one order of magnitude, but I'm guessing that the sweet spot on the Martian terrain, is somewhere in the neighborhood of 500 meters to 4000 meters wide for a given face.
As you can see that would be less than a pixel (at best) to 4 pixels, if we were looking at 1km/pixel as in the Clementine images (all the way to fractional pixels at 32km/pixel).
Consider the fact that the MOC Gallery Wide Angle images are around 750m/pixel, and after all this time, no one has found a face in those.
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