How can we change the result size for Ajax query in Contacts

Hi

When Ajax is enabled in ‘Contacts’ module , ‘Assigned To’ field shows only a max of 10 results. ie If we start typing 'Ser…" , it shows only ten names starting with ‘Ser…’ … though there are more names starting with “Ser…”

How can we increase this result size to show all names starting with the letters being typed?

Thanks in Advance.