On the entire issue of 'koshi', 'gamaku', 'hara' and such, the concepts can be discussed separately, but in use the entire body is a unit. I think their relevance depends on the structure of the training program to try and isolate areas for specific training than it does that they can function independtly.
There are different alignment structurs for different systems and likely different approachs for different levels of training.
There is nothing inherently wrong with having beginning training using different structures than advanced training.
A different answer is that of Wu Tai Chi Chaun. The teaching form first studied uses larger and perhaps more complex technique to work on the body principles, but the fast form, with the same over all structure, uses smaller movement prniciples with the suggestion the larger training built the interior technique for the smaller technique.
Different arts still trying to find similar answers.
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