As far as the 15% front and 5% rear, in that angle it does look odd but in most perspectives it blends relatively well, and gives a little more visibility for the mirrors.
As far the size difference, the Taurus is pretty damn big. Its also a bit fat at 4226 lbs. But it handles pretty nice, its so comfy, and the go pedal does just that. In that picture you have to keep in mind the mustang is lowered and on 17's vs. stock height and on 20's but it is a pretty decent difference. The length difference is very noticeable as well.
2003 Redfire & Black V6. Full suspension, 8.8 w/ 4.10s, tuned. 4.3L stroker + turbo capable of 550 hp soon
DD: 2015 SHO PP, 12.87 @107 1/4 mile (1.8 60') on 93 octane tune/CAI only. SAE corrected: 369.4/451.4 on E20, full Bolt On