i have been working on these books for a while too and its ridiculous rng!!! i hate to say it but most of my HQ came at around 18% ...
after spending millions on off hands, materia, new hands, feet ,legs and then gearing all up to be the best i could for the 4 star book attempts to find the horrible rng at this is making me cry. i have done every book except cooking and alchemy so far... and spent hours on each book and got to the point if i got to 10 stacks i just went for it and hoped for hell sometimes its worked and sometimes it hasn't. the cooking book so far i have gotten 6 attempts at 47% upto 85% and every single one of them turned out nq... thats when i had to walk away from trying for a while