I can imagine some effects, but am more curious about some real data.

I am sure there is lots of info to find about the topic, but I think the language boundary prevents me from searching with the correct words.

The thing to remember is any structure that is large relative to the sound wavelengths in question becomes a boundary to those waves, so for example the speaker baffle itself is a boundary for high frequencies, and a big enough stack of subs will also act as a boundary to themselves starting at the highest frequencies of operation(shortest wavelengths) first and extending down as the stack grows in size. 

You may have seen the horn extensions used on some horn subs, there is a similar concept called barn doors that can be used with any style of speaker system that does somewhat act as a boundary, the extent to which it works very much depends on the size of that structure. 

I am aware of those papers/writeups but am more targeting to the boundary effect a fixed concrete stage can have where the subs are placed in a special cavity. 

In a local club they have a special brick housing around some MTL2's and am curious of there are any measurements about similar situations.