The easiest way to lower rejects is to ping each one of the servers and choose 2 or 3 with the lowest ping... Add the lowest as primary and the other as failover-only.
Wait for an hour and then monitor your miner to see what's the percentage of rejected shares. Rotate the servers above if needed until you get it.
AND NEVER USE WIRELESS ... unless you can not mine otherwise
I had the it pointed at the asia server but was losing loads of shares due to disconnects, So Its now pointed at the default server which has a very high ping, Don't have much chance, It keeps losing shares due to disconnects.