To make a speaker with narrow directivity and a smooth transition in off axis response from woofer to tweeter, you generally have to crossover very near the woofer's break up region. The more narrow your waveguide's directivity, the nearer the woofer's break up will be to the crossover.
The top graph is polar response in 11.25 degree steps of the 10" Dayton waveguide, which the speaker is designed around, loaded by the Selenium D220t.
The initial "Rim Resonance" and how the woofer handles it is crucial in these types of designs. Finding the best woofer or even a good one is currently impossible using published graphs.
The second graph is of a woofer's polar response--not a particularly nice one. The next is after a make shift notch filter is added in line.
Then we have the respective responses after the low pass filter is added.
The final 2 graphs show what happens to those responses when the Waveguide is added. If the woofer's break up is as nasty as this one's, all is not lost as I'll demonstrate later.
You can see that a perfect off axis transition is impossible with this combination in its present state. The notch filter does improve it however.