I don't have Dynaudio C1 but do have Dynaudio Mirage (WMTMW configuration) which have the Esotar tweeters. These are excellent tweeters, amongst the very best. I have no problem with rolled off highs, in fact I added foam around the baffle for the tweeter enclosure to ensure minimized refractions from that surface.
My first question is whether or not you have broken them in yet, at least 100hrs would be my suggestion.
My first question is whether or not you have broken them in yet, at least 100hrs would be my suggestion.