I have no experience with this plugin, but after a look at the source code, I figured it out.

You have to call the plugin for each curve with a single equation like this:

Then use the cos() equation and the sin() + cos() equation with same start/end/step parameters.

With two equations the first one is used for X values and the second for Y values.

This explains your result, you have a circle with radius 100.

Check this with start=0, end=180, this results in a half circle.

Armin