Just revisiting the perspective theory around ellipses. So the crucial things are:
- Decide on a horizon line and the vanishing point.
- Make sure you know where the centre line is throught the object.
- Make sure the ellipses are equal on both sides and the peak of the curve on either side horizontally aligns.
- Remember you see more of the front half of the ellipse than the further half.
- The curve will get flatter the closer it gets to the eye line.