Pb with responsive image sizes in WP 4.4

Hi,

I can’t get the way to customize responsive sizes images in WP 4.4.1 :
The only available hooks that i see are wp_calculate_image_srcset and wp_calculate_image_sizes, and none of them has the named image size that was asked for as a parameter. So that would mean that you can correct image sizes, but with no knowledge of the context ?
One simple case :
One banner, 3 image sizes : mobile (780×200), tablet (980×250) and “desktop” (1600×300).
What i want is to be able to tell WP core that i want those dimensions at width w1, w2 and w3 (which would be here 0-780, 781-980 and 981+), or that i want the named image size mobile for w1, tablet for w2 and desktop for w3.

Anyone has a clue ?

Thanks