Lower crossover point =better directivity
The directivity mismatch between differently sized direct radiators will exist at any practical frequency. Cross a 28mm tweeter low enough and its output is extremely wide, while the woofer is naturally very narrow. If you cross it high, the woofer directivity has narrowed, and eventually becomes irregular due to cone break up.
Robust tweeters like this SEAS unit permit designers to make two ways with larger and larger midwoofers, but this is not an approach motivated by the pursuit of smooth off axis response. For me, I would rather have a 40 dollar tweeter and a 80 dollar midrange than any 300 dollar tweeter.