This article explains the settings and values for the Corona Render Spline tag.
Floatingpagetoc
Overview
...
Section
Column
width
50%
The Corona Render Spline tag is a solution to provide the ability to render a spline (or group of) without having to create a new geometry object so the line can be visible to the renderer. This is a render-time effect, so the final look of the spline won't be visible in the viewport.