The concept is for delayed arriving sound to help add hall ambience, solidify the soundstage, and in my case improve treble dispersion - not to modify the primary character/presentation of the main speaker. This should be more subtle than the more common rear or top mounted tweeters and is different than omni-directional, di-pole, or bi-pole designs. If I had to hazard a guess, I'd say the tweeters contribute less than 10% to the total sound.
Yes, I just listen and "enjoy" learning the speaker through break-in, but the Dayton DC28F-8 tweeters seem to make some material seem "plenty" bright, but my speakers use a single 8 inch driver (the Fostex F200A, $525 each when still available, AlNiCo magnet, no whizzer cone) that are rated 30 - 20,000 Hz, so anything above >4,000 Hz starts to "beam". In floor standing transmission line cabinets they are more bass than treble oriented, with a rich/full bodied sound - definitely not your typical thin/shouty single driver presentation - so my 59 year old ears are surely conditioned by now to less treble than most. But overall it's a beneficial effect and one I may want to tweak by trying different speaker locations and/or swapping out different caps (Duke had suggested trying 1 - 3 uF).
Based on these speakers Duke suggested an ordinary 1.5 uF poly cap (at a friend's recommendation I bought Jantzen metallized polypropylene) in series with the tweeter and running it parallel with the mains. The tweeters are rated down to 1,300 Hz (Fs = 834 Hz), as an complete electrical dunce I don't know what frequency/slope they crossover.
I believe in break-in, but of both components and via re-conditioning of our hearing. Reportedly the F200A takes 500+ hours to break-in, but have no idea how anyone would know that for sure. From what little I know the TS driver parameters should be pretty well established after 20 hours.