@cheapphenonline My guess: lower rep ranges are loaded much heavier, and are more difficult to recover from. As such, a bad night of sleep can easily mess with your top set performance. On the other hand, 8-12 reps isn't all too fatiguing so progress comes easier on those sets.
@paulsimmonds60 I partially agree — some of this new age long-length partial movements seems very gimmicky and I doubt its safety and/or effectiveness in the long run, but also, this stuff serves as new ways to progress for more advanced trainees.