Erin did that in his review of the KEF R2c and you can check the data. Unsurpsisingly, the speaker does not change much in response; that´s the nature of concentric-coaxial drivers, as they provide a fairly symetric dispersion on the vertical and horizontal axis.
That said, I wonder how the Perlisten center speakers work. They provide the data, but I´d rather see tests done by an outise source. Their driver array with a vary small mid, tweeter and mid does seem to offer a quite different result than a conventional MTM. In fact, I´m quite surprised the Perlistens show a frequency graph so similar to a KEF...
I had a look, and I am not sure what comparison or data you are referring to that will help me answer my question?