The second edition of Mark Powell's Deco for Divers, 2014, has a long chapter 2, Decompression Principles. Tissue compartments, tissue half-lives, supersaturation, critical supersaturation, and M-values are all discussed. There is no mention of gradient factors.
Gradient factors are discussed over 2 1/2 pages in chapter 6, Deep Stops and Bubble Models. GFs are described as a way to increase safety by staying further away from the M-value. There is no specific discussion regarding choosing a GF low lower than the GF high. An excessively low GF low is discussed as potentially resulting in continuing on-gassing of slower compartments, requiring longer shallow decompression to clear. I get the impression that a low GF low is largely a remnant of Pyle stops and bubble models. Perhaps a third edition of Deco for Divers would have an expanded discussion of gradient factors, incorporating more recent information.
See the article by Doolette that I cited in post #8
I am no expert and am only interested in and have followed the topic. Personally, I only do light back gas deco on approximately 5% of my dives of almost always less that 10 min. I have had no stops deeper than 10 ft. I would be glad to see more discussion.