Do you control PHP and MySQL on the server? If not then you can not set it to 3 and in fact it is recommended NOT to set it to 3 as it will impact performance of the system. If you're on a shared host provider then I know you can't search for 3 character as they won't enable it for performance reasons.

That said, yes the new FULL TEXT search is a bit different and Rick has said a few times he hope to revisit the search maybe in 7.3 and offer different methods.