background images not appearing on iPad and mobile devices

I'm using the background image feature for the homepage background. Although there are resized images for tablets and mobile devices in the template, they do not appear on those devices when viewed. I tried changing the size limits in the layouts portion of the template configuration, but nothing worked. Have I overlooked a setting?

Joomla 3.2
Blaup
Gavern 3.9.2

Could You please post an url to your site?

I sent a PM with the address to the site.
Thanks.

Im not quite sure what you would like to do - on desktop there is max width parameter which forces the background to be shown outside content column - just because content column is limited. But when displaying on tablet/mobile - then content fills full width of the page so background is just invisible.

I would like the tablet-sized background image to appear behind the Image Show GK4 when viewed on tablets. Is this possible?
Thanks.

If you haven't change much, there is already code doing that. Please check the folder:
templates/gk_bluap/images/
there are 3 files:
bg.jpg
bg_smaller.jpg
bg_small_tablet.jpg

last one is used when small resoltion screen is in use.

Yes, I already changed those images (sized exactly as they were in the demo) but the imageshow GK4 is not transparent when in tablet or mobile view.

I have tested it carefully... and I'm not quite sure how you test it - if you do it with browser resizing, bare in mind that not only width but also height is taking to consider when loading conditional tablet/mobile css files.
But the other thing that might be misleading is that image is stretched to full content width - thats why it looks strange. Its due to background-size: cover css class.
If you would like the image not to scale but just show on top you need also to decide what will render after that image - one way is to use solid color and image attached to top of the page, other way is to use image big enough and fix it on the screen.
Which way would you like it to be?

I found this also and can confirm Bonaventure's observations.. BUT I found hundreds of these in my Apache Error Log:

[error] [client xxx.xx.xx.xxx] File does not exist: /domains/p/l/player.mydomain.com/public_html/images/bg_smaller.jpg

Note that something was expecting it to be found in the main Joomla /images folder.

As a work around I copied the bg_*.jpg into the Joomla /images folder.

It is a strange place for a file that's name suggests it should be in template/images folder. You might search for a place where it is used by removing it back and then loading your site with firebug/chrome devtools developer's console open and check its error page for missing files (in chrome you will see red exclamation mark and after clicking you will find all problems on your page).