Here is a revised damage chart for the Plasma Snare. The OP manual is not correct. I used Taldren's basic range bracket styles, but most people know to stop at .99 of a range to get the true damage inflicted, i.e. range 10 is really 9.99. There was some variance on damage at the bracket ends, but I would chalk that up to the model and the placement of the Plasma launchers on the ship (what I mean by this is that I would fire two different Plasma E's from the same range and get two different damage values, but it was not consistant).
Range:
0 to 10 = 20 damage
11 to 15 = 14 damage
16 to 20 = 10 damage
21 to 23 = 6 damage
24 = 3 damage
25 = 1 damage