I my former company, they had a flaw in the bonus plan, so that a manager could give all employees maximum rating and then the bonus budget would be taken out of the pool for the entire company.
Some managers gave their employees honest/balanced reviews and were shocked to discover that all of their employees got under-payed. You see, everybody got 200%, so the bonus had to be tuned down. Result was that employees with 100% rating got miserable amounts and wanted to kill their honest managers.
I was federal as well. My first job had a set number of cases that had to met, and your rating was so determined. But they would only give 5% of the workforce an 'Outstanding' rating, so when more than 5% exceeded that they would simply change the standard. Raise it so only 5% would qualify as the highest.