I wasn't aware that my request for help would evolve into this whole discusion
I am gonna make a little mod jsgme ready and try and set the distances to
1000nm - 1853km for Important and 500nm - 927km for Opportunity.
I know for myself that I am not going to try and intecept any convoy or single freighter beyond those ranges, the chance of missing them is to great and I could have missed out on others while racing around chasing contacts in the far distance.
I don't know wether these distances are realistic but I could imagine that contacts that far away from you would be transmitted to other subs that are closer to them or allready patroling that area.
One question though......
Could I enable a mod like this during an ongoing patrol or should I wait untill I'm back in port ? I just started my 5th patrol on this career and things look rather good

so I don't want to break off this patrol.
Cheers and thank you very much for your great help....all of you