Don't have my copy of AoE to hand, but I recall the presented model is the simplified approximation, which is based on the idealised Shockley diode equation. Start by understanding that if you're keen to learn more.
The reverse saturation current (I_s) is a key parameter, but it can vary by quite a bit between actual transistors, and there are many other factors that affect the operating currents. As a result, Spice software tends to use the Gummel-Poon model to give a better approximation, but that's a bit more complicated. (Looks up "Gummel plot" as well. They're a very good way to understand BJTs. Surprised Dave hasn't done a video on it yet...)
If you really want to go down the rabbit hole, I'd suggest getting a copy of "Integrated Electronics: Analog and Digital Circuits and Systems" by Millman and Halkias. Secondhand copies are cheap, and it covers all the theory that Horowitz and Hill gloss over.