This might help you. When aligning a starter/flexplate and checking engagement, I like to start a video on my spartphone and lay it directly underneath the starter so the camera lens is looking straight up and filming where the starter and flexplate engage. This may take a try or two to get right. Then I go to start the car. Then watch the video back in slomo so I can see exactly what’s happening. Make adjustments as needed. This helped a few times. Any iPhone made in the last few years will have enough definition to do this well. Just an idea. Good luck.