I noticed that the S1223 was all over the East competition this year. Planes not using it were in the minority.

However, I'm not sure that it's the right choice in a competition where the area is not limited, like this year. You can get more lift with more area as well as more Cl. It looked like some teams had wings that were actually too large for the engine - when using this airfoil.

My hypothesis is that the same wing planforms would have been more succesful with a less cambered airfoil. The price for the high max Cl on the S1223 is high profile drag at low angles of attack. Some teams had really big wings of high aspect ratio, that looked good on the ground, but didn't get out of ground effect. This is my explanation for that. Even when getting off the ground at high angle of attack, and letting the plane gain speed didn't help, because the drag stayed too high due to the airfoil drag.

At the very least, I'd hinge the whole TE and see if less camber and less drag would help.