The property tool is meant for applying properties to particles, not the air. Maybe a separate tool?
The air can be properties of particles in 4x4 pixel.
..and the tool separating is unnecessary.
Okay, the PROP tool is meant applying properties to particles that belong to particles layer, not to pressure that belong to pressure/velocity layer. For this reason, my suggest is wrong from start.
Now become the tool separation is necessary :-P