Closed stance works for Eastern type grips because their contact point is closer than that of a semi-Western/Western grip. Because Eastern generates a flatter-type stroke, there's no real need to open up the stance so much. The topspin from a Eastern stroke tends to bounce at the other person and dips low, rather than bouncing really high. With Eastern, the goal is to hit deep, low, and with good court angling.
I hit my stroke, extreme Eastern, with a mostly closed stance. I will open it up just a tiny bit so I can hit the ball more in front of me. But I can generate topspin with a closed stance for as long as I don't wait for the ball to dip too low for my comfort zone.