The slider turns round at the dead centre

The slider's position against the crank angle, through the dead centre. The curve has a maximum there — that is what a dead centre is — so the slider *retreats* on both sides of it, and the latch works because a mechanism resting past the top of this curve has to be pushed back up it before anything can move. Set 4° past, the slider is 71 µm below the peak, and because the curve is quadratic there, doubling the setting quadruples the depth.