jcarcopo - i suspect the tweeters are the same in all these speakers, except for the waveguides being different. the encore's and the di/se's seem to have the same waveguide, while the ulfberht's and the moab's have the same waveguide. and, while i'm not sure, i also suspect the spacing has to do with the adjacent woofers/midwoofers. the smaller waveguide tweeters are adjacent to the single midwoofers, while the tweeters w/the larger waveguides are adjacent to either 12" woofers, or a pair of midwoofers. (or 10"/12"/15" woofers of the perfect set's).
and yes, if you were to build the encores w/a woofer at the top, you would want a taller cabinet; i believe the custom encore i heard about was installed in a cabinet similar to the taller moab cabinet. of course, you could always raise the cabinets. years ago, i owned a pair of coincident victory's, (great speakers, btw), and they sounded better when raised ~14" - which then had them mimicking the super-victory's but w/o the additional side-firing woofers. raising those speakers considerably enhanced the soundstaging, and i'm certain the same would apply to encores w/standard 62" cabinets, but one woofer at the top of the array... if my calcs are correct, the center of the present encore's middle tweeter is ~44.6" above the floor, or a mite higher if the speaker has spikes or feet.