All of the competitive source relate the issue to a wet chamber causing the shot displacement, not the bedding, the following form the 1970 "Target Rifle Shooting", by E.G.B. Reynolds and Robin Fulton, two names accuracy minded Enfield fans should recognize:
" water on a cartridge case of in a rifle chamber acts like a lubricant in much the same way as oil. When present a cartridge case cannot grip the inner surface of the chamber, resulting in greatly increased pressure on the face of the bolt-head. This inevitably has some effect on the vibratory behavior of the barrel and action, and influences the departure of the bullet.
In the case of rifles with Lee Enfield type actions such as the No 4 rifle, the locking lugs are about 4 inches behind the bolt face........It can increase the angel of projection on the No 4 action by as much as 4 to 5 inches, though this varies between rifles."
This is all on page 130 to 131, a lot more detail is given, and plates 55 and 56, between pages 136 and 137 illustrate how to keep ones action and ammunition dry during a storm, the demo weapon in a No 4.
I believe if folks are interested it is also in one of Sweets books, I have not bothered to check.
Common knowledge in the days of the 303 competition, now lost but for occasional forgotten and dusty tomes from the era.