The overshoot of a Fourier series near a jump is the extra height as n \rightarrow\infty of the biggest lump moving toward the jump.

The overshoot is proportional to the size of the jump. The constant of proportionality is \text{Si}(\pi)/\pi-1/2 \approx 8.95\% .
We see this in the graph below-- there is a bigger lump moving toward the second jump.