I noticed that you're not checking the two book spawns once you jump down. Each spawn has a 10% chance of being there, and at least on PvE, those books still go for quite a bit.
First book is located between the third pack you kill after entering, and the big tree in the south west corner. It's down at the flat area between the pillar (next to the pack) and the tree.
Second book is located a bit east of the fourth pack you're killing, right behind a root and right next to some of the big lashers. It is possible to LoS loot the book, by keeping your back to the root and slowly going around until it's lootable. This may take a few tries to get right.
Also, if you use Inner Focus on the very first pack, you'll have it for a second use on the fourth pack (or there about). I usually complete five runs in 30 minutes, giving me time to sort some RL stuff inbetween farm sessions.
Have fun farming