i applaud your quest for information via research. i have that book, and it's solid.
however, years of empirical data on this forum collected through thousands of hours of dyno and street tuning time have shown that subarus tend to prefer a richer afr, and slightly more advanced timing.
on 93 octane, mid 11 afrs are good. lower octane demands afrs in the high 10s for best torque output.
10.8 is not "crazy rich" on a subaru. what works on a 4g63 or an sr20 does not work on an ej2xx. there are myriad theories as to why this is the case (bore/stroke, rod ratio, manifold lengths, head design, etc) but regardless of "why" the fact remains.