What do you mean by horizontal body? That the thruster aligns more closely with the ship's center of mass?
[aaand the forum crops the image ]
These are lines of action. Orange is the engine trail, blue the main body, green the upper arms, red the lower arm, magenta the turrets and bullets.
The top image (non-tilted) has clean lines of action, but the figure is not balanced. Imbalance is not undesirable in general (in animation), but it is undesirable in this case since we associate the center of balance with the line of action of the thrusters (orange) for space ships with a single thruster.
The middle image (tilted) has its orange line of action in aligned with the center of mass / center of balance, but the orange and blue lines of action are no longer aligned. Many aesthetic elements of Homeworld ships (especially near the thrusters) are always aligned vertically or horizontally with the orange line of action. The trapezoidal structures attached to the port and starboard side of Vaygr fighters are such elements. "Blue" elements which to not align with the orange line of action look out of place; look unauthentic. No matter how much you fiddle with other elements, this misalignment won't look right.
The bottom image is what I keep suggesting. Orange and blue lines of action remain aligned, but the green and red lines of action have been shifted so the overall center of balance aligns with the orange line of action. And I think it is still possible to create the bird-like shape you're now focusing on. The red and green lines of action don't necessarily need to meet at the same place to shift the center of balance in line with the orange (and blue) lines of action.