It seems that some aspects of living room sound reflections have not yet been fully explained. As a general rule, I have always considered that floor and ceiling reflections are unnecessary or even detrimental to achieving perfect sound at the listening spot. However, there are numerous examples that challenge this belief.
One obvious example is CBT, where part of the sound is directed upwards. Another example, not yet fully explained to me, is the Linkwitz LXMini DIY, which was measured here:
https://www.erinsaudiocorner.com/loudspeakers/linkwitz_lx_mini/ (with Erin comments). The same applies to the TiFi Elf, measured here:
https://tifi.ee/en/content/10-elf-spinorama. (In TiFi's assortment, there are other speakers that have a much more ideal sound profile than the Elf. Still, the Elf is preferred in listening sessions with a ratio of 95% vs. 5%. There may be other reasons, but it could also be a difference in the vertical HF reflection profile. But can not prove...) The final aspect to consider is Dolby Atmos. I suspect that there was some non-public research behind the selection of the height dimension. Of course, these are all speculations.
The unexplained part is what makes the audio field so interesting, expect as much the "Everything affects everything" when designing speakers.
