@bshaw my room is 12 X 18 but my speakers are along the long wall (yes, sacrilege), so i have a similar depth issue as you. My speakers are WAY out from the back wall nevertheless. (Over 4 feet). This is the result of lots and lots of experimentation. I've probably tried 75 different speaker/listening position combinations.
Don't be afraid to pull them way out. In fact, try this: start with them all the way out to almost your listening position, and then start moving them toward the back wall, 8 inches or so at a time. Keep them pointed forward (no toe in) the whole time. At some point, the soundstage will snap into place. Once you know they can produce a soundstage, then you can fiddle with toe-in. I do not subscribe to the view that toe-in should be used to generate a soundstage where your speakers otherwise cannot create one.
You may decide you want them closer to the back wall than the above ends up putting them, but you will know your outer limit this way. I did this after my speakers were already dialed in, as an experiment, and I ended up putting them back where I had originally put them, but the above process resulted in a placement within 3-4 inches of what I am convinced is their best spot. The soundstage is huge, wide, and tall.