Remove top "frame" in fixed frame layout

give this a chance ( remove the other code ):

html.html_av-framed-box {
  padding-top: 0 !important;
}

.av-frame.av-frame-top.av-frame-vert {
  height: 0 !important;
}

But now you have decided to have the stretched Layout:
_____
Yes – you have to think about that, and it happens even with experienced users.
So my recommendation: as long as you are still working on the site, trying out different stylings and css settings, turn off all caching you have influence on. So the merging of the css and js files in Enfold and also turn off caching plugins. The browser cache can be hard refreshed relatively quickly with key combinations depending on the browser.
As soon as this phase is finished, you can take care of the performance.

PS: Any image larger than 2560px will be scaled by wordpress during upload and saved as original with the name xyz-scaled.jpg.
So in order not to inflate your upload unnecessarily, you should not upload images larger than 2560px.
And you should choose a higher compression rate in your graphics program when saving.
Unfortunately, the Enfold calculated image formats have no more compression, so it can happen that the original file has less filesize than the 1500px image from Enfold.

There are only a few images ( monochrome gradients – like sunsets or skin tones )where it could really be noticeable.
But you gain quite a bit in performance. It is of little use if your pictures look sharp and beautiful, but take 10s to load. Then the viewers of the pictures are already gone.

There are some snippets to avoid that and define a compression rate for those recalculated Images on upload.
This snippet in your child-theme functions.php set the compression rate to 55 ( instead of 100 : no compression )

add_filter("avf_jpeg_quality", "avf_set_quality_mod", 9999, 1);
add_filter("avf_wp_editor_set_quality", "avf_set_quality_mod", 9999, 1);
function avf_set_quality_mod($quality) { $quality = 55; return $quality;}