Sorry, but I can't give you any exact numbers. Renditioner was designed to be a bit more simplistic rather than getting into the most accurate... That said, there are two options.
First, if you really want more exact stuff, you can probably get an IES file for the light, and although Renditioner doesn't work with IES lights we have another product called TurboCAD, and TurboCAD Pro does allow you to assign an IES file to a light and render the scene (it also reads SketchUp files, so little to no rework).
Second, if you want to try it in Renditioner, I would do a test scene. Add a ceiling spot light, then directly below it on the floor try adding a series of circles. For the circles to render you add different colors or materials to each band. If you draw a line from the light to the floor and another line from the line to the circle you can use the protractor to figure out where 30 degrees is. Then just do a few quick test renders changing the cone width (I would start with it at about 40-50% of the way from the left and adjust from there.
To really mimic the light a bit better and soften the edge some (because our lights don't provide the accurate level of fall-off for this light), you could add a second point light at the same location. Have one be stronger annd the second one can have a wider cone width and be weaker. This way you might better mimic the lighting.
Sorry I couldn't give you an easier answer.