This is how I feed ~30 BPs, so yes, very consistent.I offer the rat by holding it by the scruff (behind the shoulders) with tongs, which directs it headfirst toward the snake. It could be that you aren't heating the head enough, or that the body isn't truly room temp yet, so the head is cooling faster when you remove the heat.
Add: The best part is, now my BPs are "trained" to the hairdryer. If they aren't front and center, halfway out of their hides, within a minute or two of turning it on, they aren't hungry and I don't waste my time even offering to that snake.