It is common sense Markus, if a BP is an ambush predator, then why would it always actively hunt for food like you imply?
I imagine they come out of their hides at dusk to warm up and follow the scent or trail of their prey, then they hunker down and wait for a passing food item, the essence of ambush.
I don't see it being much of a forager as they show little response to pinks and fuzzies when offered, and a gerbil would attack the snake that invaded it's nest. I'm very sure there are some that do it, but it isnt the main strategy used by BP's.
For as slow as the metabolic usage is of this snake, the expenditure of energy from actively following prey and foraging is far fetched in my mind.