I'm (unfortunatly enough) also studying Davies convolution...
In this instance I think he's right because shortly before supersonic subsonic aircraft experience the so-called "tuck under", the nose goes down and goes steeper and steeper, because of increasing effectiveness.
Maybe your RAF manual, of which I have never heard, is refering to some other aircraft. In which year has it been (re)issued? It basically comes to the profile and other aerodynamical properties of your aircraft. As soon as you have pressure changes over the airfoil you get different reactions.
But I'm no aerodynamical expert - hence I have to continue to study Davies
Dani