I think it's pretty normal that you don't hit 50 percent like that.
It's the same thing in European football,....you can win 3 games, lose 3 games en play 3 ties.
After 9 matches you will have 12 points of the 27.
The "problem" here is that you are kind of comparing apples with oranges. What Benny is noting is that the ratio percentage reflects a win percentage off of a base of total games and gives no credit to draws.
Now, one could argue that the similarities between Stratego and chess could motivate a scoring system similar to what chess uses (1 point for a win, 0.5 points for a draw, 0 points for a loss). Given that Stratego is mostly played 1-v-1 with limited - if any - spectator considerations, this chess based scoring system might be intriguing and a more "accurate" reflection of ability (notwithstanding the rating option).
A system like that sometimes used in soccer (i.e., non-American football) may award 3 points for a win, 1 point for a draw, and 0 points for a loss. This gets to your score of 12 points out of a maximum possible 27 points, or 44.44 % (< 50%). This system (which, by the way, has also been copied in some chess tournaments under what we call "Bilbao rules") is usually used where spectator entertainment is important. The idea is to motivate more competition and desire to win (or take risks to win). It often also works best in tournament settings where each game is not just isolated, but affects your prospects in a greater competition (e.g., moving to later rounds, winning a tournament).
Given Stratego here is played mostly 1-v-1 in isolated games with no spectators, this Bilbao system is probably not needed or useful. A "traditional" chess scoring system then might be more applicable (debatable).
Either way, perhaps the term "ratio" should be replaced by "win percentage" to be clearer?!