Narrow-band peaks and dips which occur within about 1/3 octave of one another tend to be "averaged" by the ear. Therefore, that on-axis frequency response graph looks far worse to the eyes than it sounds to the ears.
The on-axis dip at 3 kHz is wide enough to survive the ear's "averaging" characteristic, BUT it corresponds with an off-axis rise in that region. So my guess is the designer put a dip at the bottom end of the tweeter’s range to compensate for an off-axis "flare". Imo this is a good design choice.
The on-axis emphasis centered around 11 kHz can be compensated for by listening off-axis.
In fact, it looks to me like at about maybe 10-20 degrees off-axis the 3 kHz dip fills in and the 11 kHz bump smooths out.
My guess is that this speaker would sound excellent with proper set-up.
Duke
Not an Alta Audio dealer