Why doesn’t the minimum drag point meet the point at the best Cl/CD polar?
&quot;Minimum drag&quot; at 2deg in image 4.3 is just minimum Cd (coefficient not force). It is the most streamlined position and you will generate the least amount of drag here, for a given speed. You won't generate much lift though, if any. In fact, if you want to fly level (ie. at 1g) you will have to fly so fast that the drag will still become expensively large. Larger that if you were to fly at a more optimum angle of 5deg.
If Cl was constant over aoa, the best Cl/Cd would indeed occur at minimum Cd. ( a fixed quantity divided by the smallest ammount), alas Cl and Cd both increase with increasing aoa, reaching a best Cl/Cd ratio (in your example) at 5deg in image 4.7.
After that point, the Cd will increase a lot more than Cl, thus making the ratio worse.