as scotch said, you need to fall from a specific height for a bhop to work. In this case, on jump_core, both of those bhops requires you to hit the ceiling in order to fall to the ground from the correct height. As for the bhop itself, all you need to do is press jump at the right time (don't hold crouch). The timing is very tight so it was pretty lucky that I hit both of them flawlessly in my run.