On the Compensation screen for the employee the Base Salary and the Home Family Size specified will be used in determining what data line item of the ECA data will be used. Here is a legend of how family size will be used:
HOME_FAMILY_SIZE = 1 THEN 'S0'
HOME_FAMILY_SIZE = 2 THEN 'M0'
HOME_FAMILY_SIZE = 3 THEN 'M1'
HOME_FAMILY_SIZE = 4 THEN 'M2'
HOME_FAMILY_SIZE = 5 THEN 'M3'
HOME_FAMILY_SIZE = 6 THEN 'M4'
HOME_FAMILY_SIZE = 7+ THEN 'M5'
