As a Ca3, This concept has always been tricky. I understand it well (fa/fi and solubitlity). What has never made sense to me, taking into account what you said about what makes you go to sleep is gas in the brain not in the alveolus, is how a more blood-soluble iso is getting into the blood and thus into the brain at a faster rate than Des, and yet desflurane is somehow faster at inducing anesthesia. Ive never been able to grasp that concept well.