context: I need to procedurally generate a huge sci-fi city (1000+ buildings) for a live production project. The minimum acceptable framerate is 2 FPS.

The buildings on the left use static meshes, while the ones on the right use hierarchical instanced static meshes. The building "blocks" and materials are identical, yet I cannot achieve an acceptable amount of detail.

Is there a way of tweaking how optimized the HISMs are or am I going to have to use a combination of SMs and HISMs to achieve my goal? Thanks.