Whatever you do on that side you'll want to be able to reasonably replicate on the other side.
You can use thick, 'full fold' curtains that will do a decent job and act similarly to a 1.5" panel on the other wall.
Otherwise, you can use wooden horizontal blinds to push the reflections in the mids and highs down toward a carpeted floor or up and off the ceiling and replicate that with diffusion on the opposite wall.
Bryan