This lack of production in the shade combined with the photosensitivity for the first two years is why I’m growing mine in root pruning containers. I’ll keep them in the shade for the first two growing seasons and then plant them in full sun when they able to handle it.
If you scroll down in this thread: Pawpaw Mortality you will see some pictures of mine. I tried and experiment placing two of these first season pawpaws where they could get slightly more sun and they got scorched pretty quickly.