Just to be clear, your talking about limiting the display of embedded notes, and not the preview when hovering over a link, right?
From the top of my mind, two very different solutions come to mind. Either you limit the amount of embedded text, like @mnvwvnm is talking about, or you limit the box into which the embedded file is shown.
I’m not sure about which CSS selectors apply, but there was a similar question related to reducing the preview window recently, see Hoverover Pop up that adjusts size depending on note content - #2 by ZenMoto
Some of the same CSS could be used, I reckon, given you locate the html elements used to surround the embed.