... I don't want to just drop the idea as i am enjoying the process and the discussion around it, but i do acknowledge the criticisms my design has: several i am planning on taking a look at when i have the time.
The problem is wondering how to make the girdle area work without compromising the muscle mass there or the creatures posture - a query that is important not just for this idea, but any future 6 limbed flying vertebrate i wish to create in the future.
But on the point of it being too 'top heavy', I agree that the figure needs some adjustment, however i think you'll find that most birds are shaped in a way in which the front half is thicker then the back, but most jumping animals have more size in the back half.
(This drawing shows the basic shape my pegasi, and other animals make when in the air. the top figure is my own design (which needs reworking by the looks of things) and below are some examples of the shape Kangaroo, tree kangaroo (which is the bottom right drawing, not the mid-right one) and make horse mid jump, as well as shapes showcasing the form birds take when in flight) - Jumping animals take a different shape in the air then flighing animals, so i feel as if those requesting a larger bottem half were focusing more on its ability to jump, then its ability to fly.