Sick plan transfer after promotion question

Hello, I have an issue when an employee is promoted they go from one sick plan to another and both plans get the front-loaded accrual on the hire date. If the employee is promoted on July, 1 and their hire date isn't until Dec 1 then they won't get the new rate of the new plan until their hire date is reached (Dec,1). How can I make this happen to where when promoted to new plan the employee gets the new rate of the new plan immediately?

Thank you!