Stu: I tend to swim rather deep compared to others when I have achieved full horizontality. So the tip of the snorkel is very close to submerging, and in fact it often does, causing a disruption in my focus on smooth centred balance in whole stroke.
As a result I think I hold my face a little higher than ideal when snorkelling, which seems to me to undermine the principle of horizontality and spinal relaxation that I am trying to mold into.
Talking of molding, I have heated the snorkel in boiling water and tried to re-shape the bend angles to get a higher "periscope-depth" but it still is problematic.
I basically have not persisted in snorkel drills because of this problem. I think I will get better practice mileage just doing standard breathing drills, aiming for "just-right" timing and breathing angle, given that with my lower swimming depth I also have to angulate further for air if I don't want to risk bobbing my head end of body up and down.