…but you may also need to adjust accordingly the settings of lock screen in :
Settings → Privacy → lock screen → disable « automatic lock screen »
black screen ≠ lock screen ≠ sleep
⋅ first is « shut down » the screen ( power saving )
⋅ second is « hide your screen » and will ask for password to unhide it ( privacy )
⋅ sleep is …well almost turns off system for power saving.
Through these two menus in settings ( Power - or Energy - and Privacy ) you can link those actions and set delay between them ( after X minutes of blackscreen, lock screen is on, after Y minutes of inactivity, system goes to sleep ).