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While the drawings are certainly appreciated -- it seems the visual is causing some confusion. The variance in plane in reality is minute/tiny hardly noticeable (maybe not even noticeable without a straight edge). I believe the fall off/fall away concept -- is a newer construction tweak element, I don't do it, but I am certain there is no similarity to the dreaded 14th fret hump that is the result of an improperly made neck joint.

The way I read the pictures, you are correct, James, in that the first picture shows the hump being caused by improper neck angle. It looks like the rim/top angle is at 90deg. and the neck/heel angle is at the 90+deg required to get the correct string path.
I believe that picture two shows the correct compementary angle that gives the correct string path, and also allows the fretboard to remain flat from nut to sound hole. The fall-away is then shaped into the higher frets. So no, fall-away does not prevent the hump. Correct neck/body geometry prevents the hump, and in the fall-away, as you said, allows the strings room to oscillate.
Hopefully if I have it wrong, someone can correct me.

Alex

Oops yeah you're right!


Both pictures are exactly the same, but the first one has the angles exaggerated a lot. I think the point Hesh and others were trying to make is that the fallaway is a sharp change in the fret plane, not a bump. But still only a tiny amount, not like on the first picture.