stefanledin on "[Plugin: Responsify WP] Some problems"

Hi, the plugin is a great idea and it looks very useful, but i have some problems and I ask you if you can try to help me.
My template has the following image-classes, with different sizes:

add_theme_support( 'post-thumbnails' );
set_post_thumbnail_size( 200, 200, true );
add_image_size( 'barcelona-sq', 400, 400, true );
add_image_size( 'barcelona-xs', 294, 194, true );
add_image_size( 'barcelona-sm', 384, 253, true );
add_image_size( 'barcelona-md', 768, 506, true );
add_image_size( 'barcelona-lg', 1152, 759, true );
add_image_size( 'barcelona-md-vertical', 336, 450, true );
add_image_size( 'barcelona-full', 1440 );

Every class is used for different kind of thumbnails, but always with the same resolution. When the resolution changes, every imageclass is modified with css or html.
What i need is use your plugin to set for every imageclass, different sizes for different resolutions.
It looks like if it's possible but it doesn'r work really.
I create a setting only for "barcelona-md-vertical" ( USE WHEN - IMAGE -CLASS - barcelona-md-vertical )
And i create 4 different resolution-breakpoints using min-width and linking a new image-class with different sizes i self-created.
The form asks also the smallest size, and even if i don#t understand why i try to set it with the image-class for the smallest breakpoint and an other time with the smallest image-class size.
In both situation it takes the smaller size image for every resolution and it take only two sizes, the smaller and the original.

<img srcset="http://localhost/TgSardinien.com/wp-content/uploads/2016/05/A9-300x401.jpg 300w, http://localhost/TgSardinien.com/wp-content/uploads/2016/05/A9-336x450.jpg 336w" sizes="(min-width: 992) 336px, 300px" width="336" height="450" class="attachment-barcelona-md-vertical size-barcelona-md-vertical wp-post-image" alt="A9">
Why? What i make wrong?

Thanks
PP

https://wordpress.org/plugins/responsify-wp/