How do you zero your service rifle?

[Sunray]

"...good enough to whack a 12x12" steel plate off a bench at 200 yards was about 3 minutes too high in the offhand, I reckon..." You need to go back to the bench and sight in properly on a sighting-in paper target. The ones with the 1" squares all over it. A 12 x 12 steel plate won't tell you where your rifle is shooting.
"...meant to say that if your group is high, you'd want to lower the front sight..." The front site gets moved in the opposite direction to the direction you want the group to go. If you lower the front sight you will shoot higher.