Hourly/Salaried not visible for Hire an Employee (existing Contact record)

Summary:

While doing Hire an Employee (employee is already existing as a Contact record), I found the possible duplicate and merge the new hire with existing contact only record.

The Hourly or Salaried field under Employment is visible for normal hire but when you merge the hire with existing contact record, the field disappears. How can I make it visible?

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