I am trying to add a native ad code inside the page using Elements (on after_entry_content).
The ad code is set as “fluid” so it should take all the available width, but it get compressed to a square with ample unused space on the left; the image used in the creative is wide enough to use all the space (it is 1200 pixel wide).
You can find the example at this link; the ad is at the bottom after the ‘previous’ post link after the post content.
I have dobulechecked the Ad Unit settings on my adserver and there is no setting there that justify this behavior.
I investigated your point and I found that … I am dumb: before setting up that manual G Suite creative that I am displaying now, my Google Ad Manager account was falling back to AdSense (configured so to cover for when I don’t have a campaign) who in turn was serving a fixed 320×50.
Since the AdSense ad was a fixed size and not automatically centered, I was experimenting with the CSS to force it centered. When I finally got that GSuite fluid native creative, I forgot about the experimentation and the relative CSS code. 😀