the pilot should have put the propeller at full low pitch to help extend the glide
Sounds to me like the input from a simmer, not what we were taught flying high performance pistons. The prop can be used to modulate the descent, low pitch if overshooting, high pitch if undershooting, note the difference to your statement re low pitch. What is the ALTP rating you have, never heard of it.
I had two engine failures with the Merlin
Can you give us the registrations of the aircraft and dates on which you had your engine failures.