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
My 10 rigs have some of the lowest rejected rates posted on MC, usually under .2 %, and are running on wireless just fine.
I think the real issue is if you want to run wireless, its important to have a good quality wireless router.