Waterfall is mostly for subs FR. You want to use the impulse response for reflectionsIt’s the ETC plots i believe
https://gearspace.com/board/studio-building-acoustics/808952-how-do-i-find-my-rooms-reflections-impulse-graph.html
Looks like a great resource. I'll need a clear head to absorb and understand the concept before diving in.Thanks!