How to Default a CHAR in User defined List of Values of Numeric data type

Summary:

We enabled a list of values User defined column which is of data type number. we want to have this drop down with values A,B and C. we were able to selecte these values manually drop down.

But we also want to default these values will be employment level DFF which again holds values A,B and C. When we are using Default and override Formula we are unable to populate the values onto the LOV field. Probably because we are trying to default a CHAR into NUMERIC data type LOV.

Any suggestion on how to fix this?