Here is an example, although it is based on the Imperial Knight, the same approach can be used with the Cerasta Knight——————as much as I hate the huge chest plate (actually a shoulder plate) that looks so abrupt and out of place, I think it needs to be replaced with something else.
https://www.youtube.com/watch?v=0M-5tTB5dAw
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Let's talk about the Cerasta Knights. to make them upright, you have to modify their top-plate. this is very difficult because you need to keep their side parts as much as possible, which are their shoulders.
and you need a more reasonable chest armor.