The Kawa piston you are using has (I think) the ring stopper pin bang in the centre of the piston. Correct me if I'm wrong. this means that the ring ends will be in the centre of the boost port at the rear of the cylinder.

Although this is not a problem because of the boost port's angle it requires extra maintenence to stop the nikasil plating taking a hammering.

This is the same on the A kit RS125/250 pistons and I found we had to regularly dress up the nikasil on the port top edge with fine (1200) paper as the ring ends start to wear a groove and this can cause the plating to lift up.

Just thought that was worth mentioning.