SKILL system in game is using ELO system of counting.

[Pacifista]

The difference in the ratings between two players serves as a predictor of the outcome of a match. Two players with equal ratings who play against each other are expected to score an equal number of wins. A player whose rating is Higher greater than their opponent's is expected to win more often.

Now easier with example:

Player 1 ( 20 000 skill) kills Player 2 (5 000 skill ) will have less skill to add, then if Player 2 will kill Player 1 .

Same Player 2 ( 5 000 skill) kill Player 1 (20 000 skill) means Player 1 will loose more skill then if Player 2 would be killed by Player 1 .