Understanding and tuning the factors influencing the lifetime of confined electronic states is a basic concept of quantum mechanics, whereas achieving large lifetimes in artificial nanostructures holds great potential for advancing quantum technologies. An example of such artificial structures are CO-based quantum corrals. In this study, tunneling spectroscopy measurements reveal a strong correlation between the size of the quantum corral and spectral width, characterized by a predominant Gaussian line shape. We attribute this dominant Gaussian-shaped lifetime broadening to the interaction of surface state electrons with the corral boundary. To further investigate this phenomenon, we constructed corrals of varying wall densities. Our findings indicate that elastic processes, such as tunneling, are more sensitive to the wall density than coupling to the bulk.