During the German Spring Offensive the defences in the Arras sector concentrated its forces in the forward line. In this case it was very effective. One of the lessons learned that I have seen from the Spring Offensive on the British side was that the defensive method should fit the terrain. In Arras, with the terrain well suited to defence, a well built defensive line and troops that very much knew what they were doing, a single concentrated line worked better than an attempt to their right to copy the German system.Do you have any examples of this? Only as far as I can tell, it was pretty much universal that the front trench of a line was more of a trip wire than a fixed wall defence.
Brett Devereaux goes into the trench system in some detail (here and here),
(Courtesy Brett Devereaux. Aerial view of trench system).
In essence, most attacks in the First World War succeeded in taking the initial front-line objectives. Where they failed was in being able to push on and in being able to hold them.
In a less successful example, the commander of French Sixth Army had refused to implement defence in depth, and the initial German artillery barrage buried and broke up the defenders in many places, allowing the Germans to push through.