I just whipped up a set of wings from 3/4" plywood. They are the height of the 1.6's and 19" wide. I clamped them to the edges of my stands and played around with the angle briefly before doing some listening. So far, I'm not that impressed. I think the bass is better/fuller but they seem to have an effect on the midrange making it sound a bit more forward and nasal.
I think reducing the width and cutting vertical slits in the panel may help reduce/eliminate the problems I hear.
I couldn't resist running some numbers using a frequency generator and RatShack spl meter. The measurements were done with both channels driven and taken at my listening position:
That tip turned out to be the ticket (thank you)! Using a 1/8" sheet of recycled hardboard, I cut it out to fill in the support area one side of the stand. I first tried the board on the inside side of the speaker (closest to the tweeter panel). The results were far better than my previous attempt using the large plywood wings. Bass was noticeably improved over stock and full wing design. The imaging was slightly affected, sounding a bit closed in (like a box speaker), but I preferred the sound (tonally) with the board in place compared to no board. I then shifted the hardboard to the outside of the speaker (the bass panel side) and everything snapped into place. Awesome bass and no negative imaging effects! I haven't run any measurements yet but I can say that I no longer have a suck-out in the mid bass. Low bass is also vastly improved over stock. I'm very happy with the end result in this configuration. I'll post frequency response numbers after I get tired of listening to the music... If interested I posted a parts list with dimensions to construct the stands.