Settlement price is not using the closing price. They will compile the CI for the last 30 minutes before closing ie. start from 4.30pm. So with KLCI is published in 1 minute interval, you have 30 data. But they will ditch out the highest and lowest and left 28. Then the final settlement price will be those 28 average.
So today closing price of CI +14 1276 is not going to be used, as it is the highest.

That's why sometimes you see a lot of 1 lot done here and there as someone try to push the index a little bit higher especially at month end after 4.30pm.

So even KLCI close at 1,300, still settlement price is 1269 (I don't exactly today settlement price, as not following it as not trading it for recent few months, but roughly around that)