In his last few years Brian Cheney of VMPS was committing a number of his line source units with a lens. I never fully understood the mechanism he was working on, but the units he applied this method definitely "worked" as there was a difference with over without lens
Left no lens. Right with lens
In the link added for Graham Audio, I'm not sure, but it appears the vintage approach of slotting bass units is more of a directivity influence than what you describe for the lens
It's always an eye opener when I'm confronted with a design that "violates conventional guidelines" but actually works better.
Possibly one day I'll stumble into an audio room and the Paraline can perform its eye opener. Did that with the Unity way back machine.
