Glancing blow does not seem to reduce the stagger damage you take.

Without Glancing blow:


With Glancing blow:


Based on the wording of stagger "Blocking hits fills your stagger bar based on the damage the hit would have dealt". I feel that if you take some of the damage from a blocked hit by allocating something like glancing blow, the stagger meter should be filled less. Hopefully be filled half if you take 50% of the damage.