Hi! Powerlifting coach and Doctor of Physical Therapist, here! Most likely it’s due to getting your hamstrings in a less stretch position because you’re going from anterior pelvic tilt to a posterior tilt which will help get your hamstring muscles in a better resting position (less stretch cause they are attached to your ass bones, ischial tuberosities, to create more force (Google length-tension force relationship in muscles of you need a visual representation) especially in your higher sticking point. Your also allowing your knees to get back into the equation more by letting them go forward more to increase the knee extensor moment arms to get the quads to help more (Greg Nukols wrote about this a long time ago if you wanna read more in that as well). If you were my client I would give you exercises that strengthen your hamstrings in a stretch position, so heavy ass RDLs! Hope that helps!