That's how a swing occurs.. If you hold a seat by a margin of 10% and 3% of that margin in sliced off into a predominantly held seat by the opposition, you have lost 3% margin.
I'm not sure some of you understand the metrics of elections.
Go read Antony Green's pendulum piece. By his calculations its an 8.6% swing to Labor in WA based on the redistribution of seats and electoral boundaries.
