TL;DR: "Face the short wall" is based on a room that doesn't exist in the real world: perfect rectangle, all hard walls, no windows. In actual rooms, wall materials and geometry shift room modes unpredictably. You won't know where bass balances until you test it. Walk the room with music you know, find the even spot, and build from there. If the long wall gives you the best bass, use it. Smaller monitors make it work. "Face the short wall" is probably the most repeated piece of room setup advice