Large Tannoy Speaker Placement question:

Greetings! I have a pair of Tannoy Arden speakers (15” dual concentric; approximately 4x3x2) that I drive with a 40 watt Jolida 707 and a McIntosh 6100. My dedicated listening room (living room) is 11x18 (which extends out into 23 feet into the foyer) x 8. I have been working on speaker placement and room acoustic treatment for four years now – I use a combination of room treatments: eight nerve ceiling corner treatments and strip treatments used around the room ceiling and wall seams; ATS acoustic panels for first reflections and directly behind speakers; Echo Busters Phase 4 towers in corners behind speakers; and a RPG vari-screen behind the listening couch (the screen shortens the room to 18 feet). Speakers are positioned short wall – 4 feet from back wall and right next to left and right walls with acoustic panels on the walls next to the speakers. (Long wall placement does not yield a satisfying soundstage).
I have been working on speaker placement in this room for four years and I still don’t think I have it right. What do the rest of you Tannoy listeners do with speaker placement and room acoustics?
Shalom!