I am the most vociferous here about not having hi-fi altars between speakers. However we all have to compromise with our spaces and if you can get the equipment racked within the lower third of the speaker height that is a decent compromise.
Having said that if ( with complete sense 
) you do go for a Vivaldi short stack - I assume you mean sans silver disc transport - the boxes do need to be on individual shelves as it tells you in the user manuals.