Thanks for including the details and screenshots, @Carl_S.
Since the SmartThings Multipurpose Sensor supports the ‘Contact’ capability, you could change the Tile Layout to use the Contact Sensor Tile layout. This would give you the same look and feel as the other windows on your dashboard, but you wouldn’t be able to layer the battery on the same tile.
You could add the Thing to your dashboard a second time though and change the layout to Battery Tile - so you would end up with one tile showing the window status just like the others and another tile showing the battery status. A common approach is to create a Battery Dashboard showing the battery level of your various devices.
We don’t currently have an option to ‘hide’ the Primary Attribute in the Hero Attribute Tile (the big ‘Open’ / ‘Closed’ text on the red tile in your screenshot). You could accomplish it with Custom CSS in the new Themes and Styles feature, but the icon in the Hero Attribute Tile would not change to reflect the status of the contact sensor. We have a feature request out to add State Mapping to the Hero Attribute tiles that you may want to vote on though:
Color State Mapping for Custom Attributes