How to limit the ribbon to 2 normal size icons per column

[dschmitt]

I see. I copy/pasted your script to recreate your example ribbon. That includes the script for the 2 separators.
As you can see in my screenshot, the separators don't appear in the Ribbon. But otherwise the Ribbon script is functional.
As you know, if there would be scripting errors the Ribbon Tab would not appear. So, the script is fine. It seems Excel 2013 is ignoring the script defining the separators.

Including visibility is true doesn't make a difference.

<separator id="separator1" visible="true" />