When filling a Wilton cake pan with batter, it is generally recommended to fill it about two-thirds full. This allows enough room for the batter to rise during baking without overflowing from the sides of the pan. Overfilling a cake pan can lead to uneven baking and potential overflow in the oven resulting in a messy situation. Additionally, under-filling may result in flat or sunken cakes since there won't be enough batter for proper rising during baking. Achieving the right level of filling ensures that your cake bakes evenly, rises properly, and maintains its desired shape. It is always a good idea to refer to your specific recipe for any recommendations on pan filling levels as some recipes may differ.