The stated range was 8 reps, which would leave 6reps in the tank. Twelve reps would work with a 14RM, but not sets of 8.
Even if you look at more traditional bodybuilding programs (pretty much the definition of hypertrophy oriented programs), that vast majority of their work (probably >95% of their total training loads) is well under 80% of 1RM (think about the regular use of 20 rep squats and things of that nature).
Keep in mind he isn’t talking about an 80% load. He’s talking about 80% of an 80% load…about 64% of 1RM. My primary reason for posting was to point out that he didn’ need to make a double caclulation, just stick with % based off 1RM to avoid confusion.
Twenty rep widow makers as a final set not withstanding, bodybuilders, by and large, work in the 5-10 rep range and leave very few reps in the tank. Sets of 12 may work at 65%, but at the proposed 4 x 8, it is too light. I don’t know any bodybuilder that uses a 6 rep buffer.