True, my knowledge of animal anatomy is quite excellent. So it could be the hair is throwing its perception off for me. But I see your point about the bronco and sterno neck muscles bulging outwards due to head being orientated downward. Your judgement is better then mine by far, so I leave it at that. But I would assume you have nothing against one like me just randomly saying things like this?
I think you've found a face style that works quite nicely for a little more realism. Both Fluttershy and Pinkie Pie look very pretty, and earlier MLP generations honestly didn't even occur to me until I started reading other people's comments on your Pinkie picture.
I also really like the emphasized muscles you include, too. Gives her a more lifelike feeling, and makes me want to reach out and pet her neck, although that might sound kinda odd. Hmm, I wonder what FiM ponies would think of someone petting them.
My only potential criticism is that her ears might be slightly too far forward on her head, sorta looks like they're right above her eyes. That might be due to perspective more than anything, though.
I've got the style down. Just practicing perspective and different angles and making small tweaks
Since horse ears are very close together at the peak of the head and when combined with huge eyes they are left with really small foreheads. The perspective, with her head lowered, pushes this even further. I probably could have pushed it back slightly behind one of the hair strands that are behind the ear.