The lateral head shows a greater bias when doing extensions in an abducted shoulder position for full shortening, and reaching across the body adducting for the lengthened position. So it’s lined up when the humerus is more in the transverse plane with some relative internal rotation. The videos are easier to take in than the description.
There’s a lot of limits to EMG when just comparing means for a single muscle. Our approach is to compare the relationship between all synergistic muscles in a motion, which can help us see how the nervous system changes its bias among exercises.
We don’t have data to say what the magnitude of difference these positions make on hypertrophy still. But as I will repeatedly say, we are finding the best possible options to bias these tissues, so you’re not really taking any risk by implementing them as long as you still apply volume and effort into your training to the same degree, and follow the principles of using short vs lengthened bias movements to suit your goals.