Family instance rotation

Revit
, ,
1

Hi there.

I try to rotate some family instance made by FamilyInstance.ByFace node.

And my goal is rotate the family instances using given degree.
However, FamilyInstance.SetRotation is not working properly.

Please check the pics below and if you have any brilliant idea, please tell me that.

Thanks!!

Capture
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2

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3

before applying the rotation degree it looks okay. but as soon as i change its degree. It looks like pic above.

Capture3
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4

FYI

I found the reason.

I made faces using vector of points on line.
It has wrong value.