Hello,
We have the POWER_SAVING compile options that enables our sleep mode using the hal_sleep() function, like you say and also the OSAL power manager. Have you investigate your use case in detail with respect to Power Consumption spreadheet, Excel Spreadsheet? (for timing and battery life)
Here are a few other resources that can be interest to help narrow down where you can save battery life,
Measuring Bluetooth Low Energy Power Consumption
Coin cells and peak current draw
LPRF Rocks the World