I did install a longer plug (same design as VB supplied but 50mm) and tighten it down to 9 NM. I am surprised that it moved.
Do you guys also add carbon fiber grip paste? What torque do you put so that it does not move? I would like to know what you guys do to make sure it is secured in the fork.
I have used 10 if not 12nm on some compression plugs on some steerers, IN SITU. ie, with the stem, spacers & all already in position. The way i see it, that way, the probability that you crack the steerer is negligible, because it's working against the stem. I've also been seen to tighten the $hit out of the stem cap to remove any play. Once the stem bolts are tightened to spec, i release the stem cap tension down to 5nm or less, because at that point it's not doing anything anymore.
It took me a while to understand headset shenanigans, but once i did, i felt more empowered with my torque wrench.
Obviously, you need to have empty space between the top of your compression plug / steerer (some plugs have a lip above the steerer, others dont) and your stem cap. If there's no space / play, then you can't tighten the column.
Also, if the spacer that sits on top of the frame makes contact / too much contact with the frame, then that's a parasitic force that is preventing you from tightening the column properly, force isn't supposed to be applied there.
These plastic spacers can look like they're way off the frame before compression. After compression though, i often found them to fit just right.