[Wetzel]

The rule says "a ROBOT may not extend more than 20 in. beyond the FRAME PERIMETER (see Figure 4-2 for examples) (see G24),"
It doesn't say a total of, it says up to 20 inches beyond the frame perimeter, with no additional restrictions. The vertical extension has an additional 6 inch cylinder restriction written into the rules.

The image also shows a 20 inch box around a robot. It is all the way around, if you were only allowed 20 inches total, that box would be incorrect, it would only extend out 20 inches on one side.

To go a bit deeper into FIRST game history, there was the year that you could extend one thing out past the bumpers. Teams built a single unit arm that came outside the bumpers as individuals and were not joined outside the bumpers until fully extended. Teams were connecting the ends with string to have their mechanisms be legal. It was a mess and a headache, and FIRST does learn from mistakes and issues in the past.

Were there any head refs/lead inspectors/GDC members at the event that commented on this?

Wetzel