They also have shorter boundaries to defend against invasion. Size alone is not critical in determining a country's stability and strength, but it is a contributing factor. The ideal shape could be a circle with the capital city at the bulls eye in the middle. The compact shape is beneficial. Good communication can be more easily established.
Examples are Bulgaria, Hungary, Poland.
It's a compact country with an appendage. The Belgians created a proruption in the Congo so it would have a corridor to the Atlantic Ocean. Afghanistan also has a proruption. It was created for political purposes so Russia and Pakistan would not share a border. Namibia also in Africa has a proruption to the east called the Caprivi strip.