$2x^2$ is taller than $(1/2)x^2$ if you plot it only on a bounded segment $[-a, a]$. Also, for each b > 0, the "girth" of $2x^2$ at height b, i.e., $|x_2(b)-x_1(b)|$ where $x_1(b)\ne x_2(b)$ and $2(x_1(b))^2=2(x_2(b))^2=b$, is smaller than the analogously defined girth of $(1/2)x^2$ at height b.