Responsiveness sliders

Hi,

I have been trying out different options in the different full width sliders.

Their responsive behaviour is very beautifull, but I noticed that they always serve the same size of image no matter what the screen size( tested using chrome firebug panel and by resizing the window on my desktop).
This means my image that has to look nice full screen on my desktop, is also loaded when I use my phone. Is there a way (setting/plugin/…) to make the sliders serve resized images? I have noticed that an uploaded image is saved in 16 different sizes in the uploads folder. How can I make the full width sliders use those different sizes?

Personally I prefer the layerslider, not only because it has more options, but also because I do not like the background color of the text in the other full width sliders. But with the layerslider the text scales down on smaller screen sizes, which it does not with the other sliders. Is there a way to have the text in the layerslider readable, on smaller screen sizes?

Thanks in advance,
Sara