Ok, an alternative idea to the dropping radar distance can be this, if modding that would be harder.
We can keep the 10-15 k (whatever the exactness) of the radar distance to see other players but it can be (if it can) arranged not to be able to target them or see them on screen till 1.5 - 2K. so we would have a basic "blind" feeling that someone is coming towards us but cannot understand from which direction till its relatively close. This also applies to the attacker as well. I don't know if this can work but it is an alternative idea crossed my mind.