I created a list of 50 ribbon combobox items to test this. Using Excel 2016, I count 34 dropdown list items displayed to the user, with a scrollbar for the rest. This dropdown list height does not change relative to the Excel document window size. For instance, you can make your Excel document 1/2 the height of your screen, and the Ribbon combobox will still display a list of 34 items, extending beyond the document window.
It would be nice to have some control of this, for instance if you had a list of 100 items, but you only wanted to display the first 10 to the user, requiring the use of the scrollbar to view the remaining items. This way the list doesn't temporarily obstruct the contents of your document.
Is anyone familiar with such settings for a Ribbon combobox? Or experience working with this, alternative solution ideas? Bigger picture, I'm trying to get ActiveXObjects off my sheet's and into the Ribbon, where possible. Maybe I should keep comboboxes on the sheet? Thanks for any feedback.