Length

– If Lenght = 1 then trail particles are distributed along the entire path (1=100% of the path)

– If Length = 0.2 then trail particles are distributed along the 20% of the path (0.2 = 20%).

– If Length = 0.4 then trail particles are distributed along the 40% of the path (0.4 = 40%).

[download .blend]

– Note: at this moment, with Blender 2.8 Beta git.80ffa73b3f87 I cannot render the Halo material, so I rendered this video using Blender 2.79b