This is related to changes on Android 8 and we have no control over it/
You cannot set a notification to priority to Low to show only when notification panel is pulled down.
There is also a bug in the earlier versions of Android 8 where it always shows "App is running in the background" notification even though app has foreground notification.
Towards the end of Spring 2017 Google released Android 8 source code to their partners such As OnePlus, Sony, Samsung, HTC etc. This version of source code has the bug mentioned above. You will continue to see "App is running in the background" notification if your manufacturer did not merge updated source in to their code base regardless ACR notification setting.
You can remove this notification:
Open "Settings > Notifications > App Notifications" screen in your phone
Click the top-right three-dotted menu, click "Show system"
Click "Android System", disable the "Apps consuming battery" option