Hi!
By default the plugin uses Relevance based ordering. First of all, you need to disable this function, as it acts like the primary sorting: http://i.imgur.com/waAZFv0.png
Then on the General Options -> Ordering panel you can set up the results ordering, which will work now as the relevance based ordering is disabled: http://i.imgur.com/lPxirfc.png
This option is going to be changed in the upcoming version to make relevance and other ordering types work together more smoothly.