How can I tile the raised edges in my basement?
If you want to ensure a perfectly straight and level corner along the entire length, then I'd suggest you build a two sided "box" to rest on the raised surface.  Build it out of 1x1s, making a frame that consists of 3 long straight edges connected at perfect 90 degrees by short supports (cripples) spaced 12" on center.

Lay that box over the concrete edge, and use shims to get it perfectly level.  Glue in place.

Then apply plywood to the frame and proceed with tiling as normal.  (You don't need to ditra the box in this scenario, just tile to the ply)

Rough sketch showing cross section of wall/floor and stick diagram of proposed box framework: