That's a great space! I had no idea it was backed by a brick wall. Are there taller native ferns that would also show off against the brick wall? Are you thinking along the lines of an informal scattering of clumps to soften those lines or do you want to design a geometric pattern for a more formal planting?
If it's 13 feet from the little tree to the sidewalk, does that mean there's 26 feet between the little tree and the end up the bed near the building entrance? Or am I getting it backwards?
If you can use liriope as an edging anywhere, LMK. Otherwise I'm killing off most of what I have here, as I don't have the oomph to dig it. I forgot to mention it earlier. Jim's parents used it to edge nearly all their beds, and it worked well with the Georgian architecture of their home.