Ann: PFS Confirms LD as a Globally Significant SOP Project, page-147

If you read the quarterly in detail you see the rationale for using variable length trenches. It was a deliberate choice.
If you look at the original data from the initial trench pumping they report on 8 steady state trenches. That is more steady state data than what AMN has reported.
Just because they haven’t done things like AMN does not mean what they have done is incorrect.
Have you any evidence to support the fact all trenches must be the same length.
I would think that pump capacity might be a factor in deciding what length trench you dig to establish steady state.
Consider the situation where porosity is high, trench is long and pump is limited.
The pump would never pump enough to achieve steady state.
If the trench is long and porosity is low, a pump that can’t be tuned down could dewater a trench and make it very difficult to establish steady state.