Check out the "Exhaust_Tech(or Phase, Psi)Battleship" files in the "Particle" folder. Sorry I forgot to mention these files are only in the Sins Original "Particle" folder, but you can copy them out of that and put them in your mod's Particle folder for Entrenchment. In those files, all you need to do is increase the ParticleWidth & ParticleHieght values.

Entrenchment & Diplomacy for that matter, refer to the exhaust effects in the original Sins Particle Folder (mostly).