I have Quad ESL 63's, and have placed 2' x 2' RPG Omniffusor clones (my DIY design, using Styrofoam, ask for details if you want my instructions for them) raised on stands to be right behind the panels. They worked beautifully, but for tall electrostatics, maybe Argent Digital Lenses would work better. One way or another, I believe you're suffering from reflections of thatvery strong back wave, and could indeed "have it all" with enough effort. Good luck, and do get in touch if you want any DIY literature: I have it for Argent Room Lenses too.
Electrostatic positioning 1A
Here's a twist on this well-flogged subject: Bass vs. depth vs. midrange vs...How to restore the midrange balance when positioning speakers far off the front wall? The situation: when placed more than a few feet off the front wall the bass and depth are great (good news), but the vocal image becomes less palpable (ugh). Placement restrictions create only these two options. How do I restore the vocal presence that's there when the speakers are closer to the wall? Can we have it all?!