You need to take the minimum of the two SDF fields in the surrounding region (up to the global context if you need to) if you want it to maintain an SDF. The m

You need to take the minimum of the two SDF fields in the surrounding region (up to the global context if you need to) if you want it to maintain an SDF. The minimum of two SDFs is always a new SDF. My suspicion is that the new plane isn't an SDF anymore, that is why you are getting artifacts or your ray marcher has problems with large scope angles, or something.