I'd give a shot at drying it out even more. Overnight or a full 24 hours. I'll often leave flakes out for a couple days and then throw them in an old tin where they will get even drier as I smoke them during the week.
After trying it on several occasion and Mixture Flake as well,I gave up on these blends , nontheless more Burley forward blends of Mc Baren are more or less bearable,no doubt even those including Navy Flake are prone to bitingI suggest you try a filter pipe that worked for me.There is no way I can smoke Mac Barens Scottish mixture without a charcoal filter.