Thanks @robbieobbie
I had already thought about this.
The problem is that this will be the maximum width, resolution, for all images, including those posted on masonry mosaic in the main page. Imagine one frontpage with infinite scroll, with all your images at 1200px or more. Imagine the reading time for this page in a standard internet connection!?. The approach in using featured Images thumbnails used in posts in the main page seems correct, but when you click on any image in masonry mosaic is opened one page where the image is same Featured thumbnail image used in Posts, no matter your resolution. There is no way to open original full width image or another linked custom media or content. Ie. Clicking in images in masonry mosaic on the homepage, you open in a full width page, the same Thumbnail used in masonry mosaic, with a small field below with a short description, and to make matters worse with two scroll bars.
And looking at the code seems impossible disable this page to add any lightbox in this theme to open anything linked in featureds as a full width image or any different media.
Seems impossible to disable this full screen page showing front page’s thumbnail images. The only thing favorable for this, is that it’s fully responsive and works perfectly on mobiles.