Just had a look at the HowTo Work in Different Spaces help patch and noticed this:
I had to read the descriptive text of Position in Projection several times to get its meaning, mostly because it lacks the info that Y-axis is inverted.
Suggestion:
The smaller window dimension is in range (-1,1). The other dimesion is scaled according to the aspect ratio. Also, compared to World Position, the Y-axis i inverted.