Need to access Assignment and Salary references from the Add'l Assignment Info Autocomplete Rule

Summary:

When creating autocomplete rules on the other business objects, we're able to access various assignment and person related variable values. Now for the "Extensible Flexfields >Add'l assignment info" rule we need to access to and be able to use employee's Current Salary details. We're able to refer to "Get Assignment" row but cannot find a way to get Existing Salary.