Sorry, you are right. By default the field is set up to inherit its value from the Test Set Folder. and it is set to be Read Only.
Perhaps there is a way to enable the field for editing in a way that a blank value at the folder level would not override a value you set at the Test Set level.
If not, then you would have to move the Test Sets to separate folders.
Perhaps there is a way to enable the field for editing in a way that a blank value at the folder level would not override a value you set at the Test Set level.
If not, then you would have to move the Test Sets to separate folders.