Phil,
The more I dig into this, the more interesting it is becoming.
When you talk about the optimum length/width ratio being 2.5:1, I automatically assumed that the Streamlining Template had these ratios.
Well from the drawing below, you can see that the 2.5L dimension is at this location while drawn on top of the "template" and the yellow line representing this length is much shorter than the rendering???
If one were to extend the tail of the rendering all the way to the ground level, I'm guessing the length/width ratio would be closer to 3:1. Whoops, I'm off a little bit. Just fired up the CAD and checked. It's 3.58:1. And this length/width ratio does *not* include the nose.
If the rendering *was* actually drawn 2.5:1 in length from the maximal height, the 22 degree angle would be the predominant *curve* from the ground up towards the maximal height. Not sure what to make of it?
Unless.... your 2.5:1 ratio is for a fully revolved shape above the ground, and when this revolved shape is cut in half and brought to the road surface, the length/width ratio then becomes 5:1. If one includes the shape of the nose, then maybe the rendering is pretty close to this ratio. It's getting late, and I will check tomorrow.
Since it can be assumed that Honda did a good job designing the roof of the Insight, I went ahead and worked up the geometry of the roof shape, stopping where the tail starts.
Here is what that geometry looks like. You can't tell from this small picture, but I zoomed in real close with the CAD program to make these curves/angles, so they are very close to the actual shape of the roof.
By the way, this particular picture was shot from about 100 feet with a zoom lens, so the perspective is at a great distance, minimizing parallax error.
Jim.