How to resolve loophole with delivered rule "Validate proposed Salary Amount during Promote Action"

Summary:

"Validate proposed Salary Amount during Promote Action" is a delivered Field Validation Rule for the Salary Amount field which  validates that the proposed salary amount isn’t less than the current salary in promotion actions.

When changing the employees salary by using the Salary Amount field, the rule works as described. However, if users bypass the Salary Amount field and instead change the salary using Adjustment Amount or Adjustment Percentage fields, the rule does not execute and a decrease in salary is permitted.

When creating rules for salary BO, it does not appear we are able to author rules for the Adjustment Amount or Adjustment Percentage fields. How can we add additonal logic to close this loophole and ensure that when users change the salary using the Adjustment Amount or Adjustment Percentage fields, the rule still executes as expected?