understanding brush dynamics (angle jitter)

[Ofnuts]

"Random"  goes from 0.0 tà 1.00 (or read it as "min" to "max"). The Angle scale goes from min to max too, that is, 0 to 360°. Catch: the middle position is 180°, so the brush is upside-down!  Obviously the angle is the "trignometric" angle, which is counter-clockwise. So, top to bottom:

• The angle is constrained to 340-360°, so the same as -20°-0° CCW, which is 0°-20° clock-wise.
  
• The angle is constrained to 0°-20° CCW, so the same as -20°-0° clock-wise.
  
• The angle is constrained to 170-190° so more or less upside-down.
  

So yes, having the brush wiggle a bit around its "upright" position requires a very contrived curve, and its better to use an upside down brush:

   

   

Changing the angle range from -180° to +180° has already been suggested.