Writing as the representative of one normally very reliable groundschool, I would say that the bow shockwave forms at around M1.0 freestream, but stands off from the aircraft or wing leading edge because of the rise in temperature mentioned above. At some higher M the bow wave will move in and make contact with the LE as a normal shockwave (Mdet) then begin to become oblique as the freestream M increases. This is a simplification, as always.
Mdet gets its perverse name from the early days of supersonic research when the only way to get a supersonic wind tunnel was to pump up a huge tank of air then suddenly pull the plug, letting the air past the model at high M. As the air slowed down, the bow shock would straighten up and then detach itself from the model. Hence Mdet and not Matt.
Dick W