Calibration currently “determines” the rotational radius (radius from center of router but to the middle of the first link of the chain). You just need to put in an appropriate estimate during the calibration process. For the existing ring, it’s ~140 mm. The value you enter will be higher. You can take a look in the forum’s wiki category for a post that explains how rotational radius is measured. Use that as a guide to arrive at your estimate (I’m using my phone to reply otherwise I would have included the link to the thread)
You can’t remove handles (button in the middle of one is for disabling aretation and is possible to turn it to lever router up and down)…
Diameter of router base is 18cm