Processing and Formatting Effects > Flame FX > Matte Edge >
Matte Luminance Curve Settings

Matte Luminance Curve
  Controls the blending of the edges. You can add keyframes to the curve using Add mode, move keyframes with Move mode, and modify the curve’s shape using tangent handles.
Reset button
  Resets the matte edge curve.
Home button
  Resets the position of the matte edge curve after panning.