I think for identifying the line of action any pose is fine. I think the dynamic poses are probably actually better. Check out the ref you have with the full body suit, that is a great place to start because the LOA is on the body suit, it is the center line. This is a good start. I would say in general try to make them a bit more curvy / dynamic as your figured will be built off these in time and having a more interesting LOA will give you a more interesting character. Im still fairly new but here is how I handle the LOA on these. There is no one right way but I try to make the line interesting as possible.
Hopefully that helps, let me know if it doesnt make sense.