Need help to capture current benefit coverage amount - Postelection Edit fast formula

Hi Benefits/Fast Formula Experts,

We have a requirement of postelection edit formula to trigger the error message when the person reducing the coverage amount from the previous coverage amount. We have used ben_fn_get_char_value function to fetch the coverage amount (BNFT_AMT) and change context to differentiate the previous coverage date and current coverage date. Logs are showing both amount values are same. With the postelection edit, we wanted to capture the onscreen amount (which is being reduced from the previous coverage amount by an employee), so that it will trigger message and not allowing the user to reduce the coverage amount. Attached is the