For an example of someone who can drop very deep with a proper spine, have a look at what Akuzawa does at ~0:44 of this video:
YouTube - Akuzawa Minoru
... I saw a YT video of him doing sumo squats with his hands over his head that would make a great example of what I'm talking about, but I can't find it.
Sadly, the only good profile shot of this kind of horse stance I can find is partially obscured by a spear. Here's Chen Ziqiang (Chen Bing's little brother):
He's "sunk" into the stance, which is to say that his torso is much as it would be standing. Consequently, his ass doesn't stick out as much as it would if he were leaning forward. It's important to note, though, that he hasn't over-corrected into kyphosis (flattened lower back).