Hey Again,

If you want the whole image to show not matter what screen size you will have to use this custom css : 

Add this into the Custom CSS box located in your Salient Options panel (All custom css provided is tested in the Live Browser so it will work as intended . If you cant see any changes make sure there is no red cross in the Custom CSS Box as that syntax error would cause all css below it to not show up on the Frontend):

.post-area.col.featured_img_left.span_9 span.post-featured-img {
    background-size: contain !important;
    background-repeat: no-repeat;
    background-color: #fff !important;
}

Thanks

You cant add a Landscape image to a Portrait thumbnail so we would suggest to remove the text from the images if you want to use such a style. 

Best