Not quite sure about the explanation of the higher wing travelling faster, therefore creating more lift, and this effect being greater the higher the bank angle . . .
If you look at the two extremes, a flat, rudder only turn would result in the highest difference between the wing speeds through the air, and the closer you get to a 90deg bank, the less the difference between the wing speeds - as the hypothetical cone that B2N2 refers to becomes closer to a cylinder!