I think what you're missing is that although the 64-10 is a wider dispersion tweeter it has to be crossed over much higher in the frequency range than the 70-20. This gives speakers that employ the 70-20 the advantage of wide dispersion in the upper mids and in the treble without a crossover point in the frequency range where our hearing is the most sensitive. It also allows for better directivity integration with a midrange that hasn't started to beam yet. When you look at the 70-20 RAAL Towers against some other popular dome tweeter speakers in their price range they have significantly higher off-axis SPL from the midrange through to the treble while maintaining a smooth directivity. I think that is the real advantage of a tweeter which can crossover at a much lower frequency while also maintaining relatively low distortion. This appears to also be the strategy used by multi-way benchmark speakers like the Salon2.It seems to me something else could be at play because like I said the 70-20 in the Ascend towers isn't that wide of dispersion but since your listening tests show them to sound more spacious it's possibly because they are smoother off-axis and simply more neutral tweeters. Also, if wide dispersion was so important then you would think the 64-10 would be the best RAAL offering but I don't think I've ever heard someone claim to prefer it over the 70-20 which is more evidence to me that it's really neutrality, both on and off-axis, that is responsible for the preference.