When designing your project schema, it might be desirable to set all property fields to the same number of characters. This would produce visually appealing input fields of the same width.
However, when dealing with combo box properties, also known as domain lists, the number of characters does not play a role in defining the width of the list. This results in field length variations which may not be desired.
To resolve this, turn off Calculate List Width in the Combo Box Property page.
Note: The horizontal space for the drop down arrow is approximately two characters.
A sample OpenCities Map CONNECT Edition project schema is attached for your learning.