The collapsing directivity of the saladbowls at higher frequencies crams the decreasing power from the compression driver (all compression driver's power response starts rolling-off around 4-5khz) into a smaller angle, the result is extended response on axis. On axis mind. This is the same reason the Altec 511B has extended response. With constant directivity horns, such as the latest JBL and EVs, frequency response on axis tracks the falling power response of the compression driver and on-axis response is rolled off, thus the need for EQ (which is what compensation circuits are) with CD horns.

Personally I think that the Edgar saladbowls are superb horns and I prefer them to any horn I've used with 1" drivers except the Altec 511B, a horn which I think is just as good. And I've used lots of horns over the years, heck I still own 7 sets of horns; JBLs, Altecs, McCauleys, Edgars and PAudios.