Hello MintyMatt,
No need to worry about the size showing Medium Large, We only need the other size that we set on Setting > Media.
The Screenshot is misplaced on our documentation but the size you added it true.
The above cropped image is only work for the featured image, not for the images added on the content section.
So if you want to add the image through the content section, please manage the size there.
If you feel any confusion, please feel free to ask.
Best Regards