Spray tool behaviour seems quite unpredictable.
With flat mode on, pressure set to 1 and draw a single click then a small brush (9 pixels or less) will draw the brush once but a larger brush (10 pixels +) will draw the brush twice and even larger brushes will draw even more copies.
I’m not certain what flat mode is meant to do (I’d guess uniform brush distribution vs. naive centre-biased random distribution, eg. http://mathworld.wolfram.com/DiskPointPicking.html) but it also affects the number of brush copies drawn.
With a small brush, pressure set to 1 and draw a single click then the brush draws once with flat mode on, but the brush draws many times with flat mode off.
It’d be preferable if the behaviour was more consistent and predictable, such as pressure directly indicating the number of brush copies drawn per step and flat changing the distribution but not the number of brush copies drawn.
On a related note, the step setting is disabled for the spray tool though I think it could be useful when the user wants to draw fewer copies of a larger brush.