Thanks for your replies! I'll revisit the arrow position.
@RachelArmington This is personal project, a series of three illustrations for The Lion, the Witch and the Wardrobe. So no real binding here, although it's true that I got the dimensions from a paperback, glued copy. So I can imagine that this newly illustrated edition is deluxe! But you're right, that ear could disappear altogether.
@Nyrryl-Cadiz Well, those Greek centaurs on the vases I looked at were pretty slack, then! I was imagining that he was in the process of lifting the bow. But I do remember something like what you said during my brief experience with archery. And given that the arrow is problematic, I'll look at that again. I also feel like the centaur's arms are a little short.
Thanks again for your kind words! Onwards and upwards!