The system is designed to have the lever bleed screw displace some oil as it's reinstalled. In other words, the lever end wants to be completely full at the end, and there is not supposed to be an air gap there
In the too little fluid direction, there is some tolerance for an air gap before symptoms begin, but ideally you wouldn't have any. If by chance ...
I sent an email to Magura to ask about the insert. Their response:
Die Stützhülse ist nicht bei unseren HS Bremsleitungen zu verwenden,
hier genügen der Klemmring und die Überwurfschraube.
Für den Teilebedarf zum korrekten Leitungsanschluss helfen die
nachfolgenden Explosionszeichnungen wohl am besten weiter.
The insert isn't used ...
I assume by 'pin' you mean the following part:
This part is called the 'insert' or 'connecting insert' and its purpose is to 'support' the (non rigid) brake hose in order to prevent it from crushing/reducing drastically in diameter when the sleeve nut is tightened causing the olive to be compressed onto the brake hose.
In other words: When tightening the ...