I also tested with ‘Ground Mesh’ and the result is fine. Depending on the GS, the shape of the terrain, the desired surface settings, it can sometimes work better with ‘Ground Mesh’, and sometimes with ‘Surface Mesh’. Thanks for the advice and for the extensions!
Since I’m using the terrain model to virtually (hypothetically) reconstruct a 2000 year old fortress (as a hobby), of which only a few visible ruins remain now, and the terrain is certainly different from what existed then, the difference that may appear between the two methods of generating it may not have a major impact. Plus, I then process it to conform to data I have from the existing ruins.
Virtual reconstruction of a 2000-year-old fortress - eg: post1, post2.