Jason will stalk and pick off his victims that would
1. Not alert others to his presence
2. Seperated from the group, one-two victims at a time with little exceptions
Reasons for survivors making it to the end.
1. Safey in numbers.
2. Aware of things around them
If you look at the films Paramount were responsible for (1-8) you would find this pattern with some deviation. Examples: Part 6 Tommy was focused and aware of him being alive, the girl that survived was into Tommy so she was with him the whole time. Part 7 Tina had visions of him and the guy survived by being with her. Killing them during or after sex is getting them when they are vulnerable.