The Fiori theme is elegant, more modern than the others and most closely resembles what my users want.  However, it styles all of the elements abnormally large.  This isn't optimal for a grid based data-centric application where there is a premium on window real estate.  

Can you develop a Fiori Slim theme that is similar in appearance, but has vertical and horizontal dimensions similar to your other themes?

We have overriden many css properties to achieve this, but it is very time consuming and incomplete.