Bounding box seems to limit the amount of polygons possible (doesn't seem to affect dense cloud count - that seems entirely limited by memory). Try using detail chunks and then merging chunks together. It will retain the detail in those areas.
I had a section of a wall that was mostly flat-ish.. 2-3" deviations in depth.. nothing huge.. then there were sections I covered much more closely with many more angles that were far deeper.. I duplicated the chunk, sectioned off these "detail chunks" with smaller bounding boxes, and I re-ran them with the highest settings possible. The results were night and day. I then merged the chunks, including even the mesh, and the results were very obviously different quality in those sections.
I wish this whole process was easier, bu it does seem to work in some cases. This seems to be limited by memory.. as a dense cloud at high with a huge bounding box is nearly the exact same quality as one with a much smaller bounding box in most scenes. If you process on low, detail out areas, process them on high and merge, they will retain their quality for the final mesh generation from my experience testing.
Hope that helps!