New feature "Media Image Number"

I have a feed url ( http://www.fifa.com/newscentre/photo/rss.xml ) which contains multiple images , I want to add the large image into my database. So I tried using that via “Media Image Number” option given in feed items but its not working,I have tried all possible numbers given there.

kindly check this problem and post back .

Thanks & Regards ,
Aquib.

https://wordpress.org/plugins/wp-rss-multi-importer/