How to modify artillery units' accuracy?

[vergilyao]

For example,I want to let culverin fire in one point all the time.So I modify the descr_projectile.txt and search the line of "accuracy_vs_units" about it,change the number to 0.0001.But I find culverin still inaccurate when it fire to troops.
I doubt descr_projectile just define the accuracy of shells and there is another file define the accuracy of artillery.
Can anybody tell me how to make the culverin fire more accurate?

[Damonk]

Shouldn't the accuracy be set HIGHER rather than LOWER if you want to achieve more hits?

[MWNF]

Where'd you find the descr_projectile.txt file?