Blur content behind div tag when background centred

Blur content behind div tag when background centred

I know this has been asked before and I have been able to blur content
behind a div tag, but when the background is centred, Blur.js doesn't pick
up that the background has been centred and continues to blur it as if the
background was the full sized image.
The problem can be seen here: http://home.josephftaylor.com/cadets/