Is it possible to reduce radius of Ringworld/Sphereworld.

the physical size can be modified by changing the radius of the model in (I forget which TXT, I think it's stellar objects.)

The area disrupted by the placment generator.... I'm not sure if there's a way to change it.

You can change it. In the components that create the ringworld/sphereworld one of the abilities specifies the radius that needs to be cleared.

Then you should probably adjust the scale of the model to fit with the new radius.

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