Wall Defence Towers

Ok, In the world of modding games I am a complete noob so I only know a limited amount of what I am doing ~.^
I also have looked around the thread to try and make sure I wasn't posting a question thats already been answered so If I missed it I apologize.
I was looking at changing stats for units like siege towers and such and wanted to know how you change the range for wall towers. I know that a thread was posted for getting rid of the oil/fire defences for gateways by changing the arc of fire but I couldn't figure out how to make them shoot farther. Also, is there a way to change the fire statistics for towers like you can regular units.

Descr_walls.txt and descr_engines.txt I think contain all the information you need to change. There are tutorials about this found on the forum.

I may be wrong but you can't change the range of the wall towers in Descr_walls.txt. And if I am wrong will someone please tell me what I have to change. And descr_engines.txt only allow you to change the seige equipment used against walls. Will someone please point me in the right direction?

Descr_projectiles_new.txt can be played with, but aside from changing angle and velocity of the projectiles being fired by the walls (which may give some range boost/penalty), I can't see a direct range attribute, unlike for siege towers where the range and damage is easy to change.