@AAfh  
Honestly, I have no idea what to tell you there. The guys there might have a better idea of what to do than I do. Did you ever ask them why you shouldn’t use the show as a refrence? I’m curious as to why they said that.
 
And you don’t have to physically trace over lines to trace, there’s also freehand trace, which is just when you try to copy lines from something exactly by looking at it. It can be helpful to freehand trace sometimes, but if you really want to improve the best thing is to do full drafting, I.E. only using references to get a general idea of what you want to do and then figuring out where the lines go on your own.

@Background Pony #0BEA  
Thanks for the pointers! I did use vectors as references for a while, because /mlp/ repeatedly said not to use the show as a reference, and then later I was repeatedly chewed out for using references, so I’ve shied away from them in general. I suspect a lot of my improvement will come from unlearning pointers they gave me. I’ve started to allow myself to get more sketchy with my undersketch, for example, instead of drawing and redrawing each line until it’s perfect.
 
I’ve never traced, though; I don’t even really have a setup that would allow that.

Yay, more horses besides Twilight!
 
To be clear, I don’t mind you drawing Twilight. I just think ONLY drawing her is counterproductive if your goal here is improving.
 
That being said, I should say that the “gut” you see on the standing models isn’t a static prop, it’s part of their body. When they have their legs under them it’s going to stick out a bit, but when they pull their legs back like this it’s going to pull back and kind of flex with their bodies.
 
In that regard, you can imagine it like a bicept or something similar. When you have your arm cocked at a nintey degree angle your bicept is going to stick out more, but then when you straighten your arm out it’s going to get pulled down and flatten out a bit.
 
Here are a few examples  
 

 
See how with these the “gut” tucks up inside the thighs whereas yours projects past them quite a bit? That’s what I’m talking about.
 
Also, in general I think you might have the gradient for the shape of their guts wrong to begin with. The way you draw it their torsos are kind of “pear” shaped, with them getting thicker towards the back end and then very suddenly tapering off, whereas a “bean”, something that maintains a pretty uniform thickness with a gradual taper at both ends, is generally considered better. That might be down to the refrence you’re using though, I’m not sure.
 
I mean, that could just be the style you prefer, but in my personal opinion it doesn’t look very good.
 
I would definitley recommend that if you want to keep going for this sort of 3-d show style looking using the screencap tag here on derpi for additional references. For example, I found the examples above by searching “screencap, bucking”
 
Gifs are great for references of “subjects” in motion like this, since it lets you get an idea of what’s really going on with the subject, whereas with a static picture you might end up missing context and misinterpreting certain things.
 
As per usual, just remember with that, using references is fine so long as you’re not just tracing off of them ad nauseum, though you seem to have figured that out so I won’t keep you any longer!