nothing new, this is very famous issue
https://sound-au.com/bafflestep.htm
http://www.salksound.com/wp/?p=42
https://diyaudioprojects.com/Technical/Baffle-Step-Correction-Circuit-Calculator/
The choosing right crossover point 500-700 hz the speakers designers
easily bypass this problem and can make good result with 9-10 " wide
https://sound-au.com/bafflestep.htm
http://www.salksound.com/wp/?p=42
https://diyaudioprojects.com/Technical/Baffle-Step-Correction-Circuit-Calculator/
The choosing right crossover point 500-700 hz the speakers designers
easily bypass this problem and can make good result with 9-10 " wide