Box collision definitely the way to go here. If you use traces, you’ll have to perform trace every frame (tick) during a sword animation, and if the sword is fast or the frame rate is low, you’ll miss some locations inbetween.
With box collision you can handle fast moves by enabling CCD (continuous collision detection) somewhere in the collision parameters, which should solve that problem.
Regarding the original question, is a good question actually. I don’t have a definite answer, but here are some ideas :
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You are tracing along one of the box axis, so yes you can extend the box. But that might not always be the case. Take for example a character moving and jumping around - you have to trace the character’s capsule collision diagonally all over the place, and cannot just “extend” the shape like you did. So the “Trace 2” approach simply covers more use cases.
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You are seeing similar results in debug while hitting nothing, but the result may be different if you are actually hitting things. Again I don’t have definite answer so I’m not sure about this, but you might want to check what happens if there are two objects overlapping the sword. Your first trace will immediately hit both, so maybe there’s no guarantee in their hit order, while the second trace would hit them in consistent order. Also, the Hit Location, Hit Normal, and Hit Impact Normal values might be different in first and second traces, because in first trace the object is already overlapping with the shape right from the start, so I’m not sure if the engine would be able to figure out proper hit point and directions (to be confirmed).