Used to live in the realm of Star Fangled nuts...but recently got a Carbon fork/Steerer tube with a compression plug.
Everything is installed, but last night swapped out a new stem and while doing so, got curious how exactly the compression plug works...not to mention how to properly screw the headset cap back in: In addition to the cap and stem bolt, there's also a spring, two very little washers, and a larger/wider washer...I think i installed it all back in the proper order, but have been searching for a diagram to be sure.
FYI: I've got a FSA integrated headset and Easton 90SL fork.
Don't know what compression plug you're using, but it sounds similar to one that I used to have. So, from top to bottom, it should be cap, stem bolt, smaller washer, spring, small washer, big washer, expanding wedge part. Basically the two smaller washers are have the spring exert forces more evenly on both ends. The big washer is to prevent the wedge part from coming out when you're tightening it.