It is here with a review - click on measurements show - they have ground-plane, plus in-door polar response
I did find this review of Ascend vs HTD: http://forum.ascendacoustics.com/showthread.php?2294-170SE-vs-HTD-Level-Three-Bookshelf
I found the HTD L3 review to be quite impressive in the context of use with modern AVRs that have automated system optimization facilities such as Audyssey, MCACC or YPAO. As long as a speaker's on-axis response is reasonably smooth, room/speaker mismatches which result in suboptimal response will be zeroed out by the AVR if people take the 5 minutes or less that it takes to run the AVR's optimizer. The non-fixable secondary properties of the speaker can then shine. These are controlled directivity and low nonlinear distortion.
Here are the relevant facts:
This is the response curve of a nicely extended, relatively smooth but possibly slightly colored speaker (In some listening environments)
The broad slight dip in the midrange and slight rise above 3 KHz are the sort of things that Audyssey, MCACC or YPAO excel at managing.
Here is the good stuff that can't be equalized into a speaker:
In particular I'm looking at the family of more-or-less parallel response curves for off-axis response. This is characteristic of a speaker that has more consistent timbre in various rooms over a wider range of room acoustics and off-axis reflections.
The basic design which is flat panel tweeter mounted at the base of a waveguide is something that leading and well-known waveguide enthusiasts have been talking about at least privately for decades. It is a good idea whose time may have come.
Anther well-known and attractively priced speaker that has this property is the Behringer B2031.
I'd like to hear the HTD's but that seems unlikely.