The consensus on the forums seems to be... unclear. I think the best response is this post:
Glossary definitions from PHB (for Arcane Reach) and Essentials (for origin square and push).
Arcane Reach: When using a close arcane attack power, you can choose a square within 2 squares of yours as the origin square. The power still follows the rules for close attacks.
Push (forced movement): Pushing a target means that each square of the forced movement must move the target farther away from the creature or effect that is pushing it.
Origin Square: The square where an effect originates. Every power has an origin square. A power's attack or utility type determines the origin square's location.
By RAW, you would push the target away from the origin square.
So if you used Thunderwave (a close blast 3) and decide that the origin square is 2 squares away from you (from the Arcane Reach feat), then any creature pushed with Thunderwave would be pushed away from the origin square (2 squares away).
Which also supports logic "origin from any square 2 squares away, thus you can attack yourself from the target line: Target: Each creature in blast, as you're a creature.