you can specify on a ship by ship basis how tarnsparent they are to be at creation, they will grow more transparent untill they are totaly invisable as the trail section grows old
there is also table based controle on the relitive width (a number that the width it is multiplyed by) of the trail, by defalt they are set to be 1/2 the diameter of the glow they come from (so if you want realy thin ones you set +Width: to be .2 wich would make them .2 the radius of the thruster they come from)
I didn't set table controle over ending width (just set it to 0), but if you all realy want it I can add it fairly easily
bitmap is controlable on a ship by ship basis