@prof I wrote a long post earlier in the Thread. On reviewing your supplied Images I can see there are similarities for the methodologies we have selected for a Sub Support chosen for the Speakers.
The Backward Tilt is not strange to myself, as nor is the forward tilt.
I'm sensing the 'Toe In' is also arranged to be optimised to the listening set up.
My set up is in a room that is solely used for Audio Purposes, which leaves me the options to use materials that are not as aesthetically neat finished as your own. We do share a like for similar materials in the assembly of the Sub Support.