I recommend Moonwalking with Einstein by Joshua Foer and A Mind for Numbers by Barbara Oakley. These books helped me better understand how people learn and how memory works.
any extra sources (books/drilling material) can always help understand approaches and that with different views, everyone learns differently so its hard to say what would work better for you
I've heard that both books go along with 7sage so if you score in LR still doesn't increase maybe look up the free chapters available on the trainer's website to see if it's something you might want to buy.
... own all the 10 Actual books plus the Cambridge PDFs 39 ... all of the 10 Actual books off of Amazon (even if ... PT I take in my books). Takes a little elbow grease ...