Header does not reduce with page

Hi .. Love the plug-in. Thanks.
Using Weaver II and newest WP.
Original site is 940 px wide and I changed it to 1000 wide.
It all works fine on the PC.
When I am on a tablet and turn it portrait, the image retains 1000 px wide but the rest of the page reduces.

Where do I need to look to control this?
Thanks
rick

http://wordpress.org/extend/plugins/cimy-header-image-rotator/