Ah! That is really helpful! So, if I understand correctly, positioning myself higher up in the above case and shooting downward into the lamb’s eye would have brought the catch light lower in the eye since that would lower the reflected horizon? Also, looking at your diagram, would having the light source at either a very obtuse or very acute angle as compared to the camera also produce a larger catch light?
So, practically, to get the catch light on a cloudy day, I need to make sure that the animal is facing the open, cloudy sky and then position myself so that I can get the reflection of that in the eye. I’m going to have to think about that math… Maybe I should set up some mirrors to experiment! Wait! Dew droplets on the grass would probably do the same thing, right?