So called constant directivity horns for example narrow its radiation between 500Hz and 1kHz, but widen it again above 1kHz(1). With the 1.5" "optimized aperture" design off axis level exceeds the on axis level by several dBs between about 3kHz and 12kHz(2). The latter combined with the narrower radiation below causes a serious inbalance.
As most people wouldn't listen on reference axis this may be an issue. At home and especially with horns the reverberant field can't cure that. To tow the speaker in isn't practical due to sheer size of common (to us) cabinets.
Thanks a lot
(1) This is true with the groundbreaking EV HR90 up to now with JBLs PTWaveguides. Not to forget E.Geddes - his famous design shows the effect too, which makes "higher order modes" a/k/a HOM apparent at a glance to the educated reader 8-]
(2) http://www.jblpro.com/pub/obsolete/23525354.pdf , "Horizontal Off Axis Response"