I always balance the plane horizontally. I don't understand nose down. How is it balanced if it is a little nose down? No idea; you can't measure the angle, and even if you could, what would it mean? I think I can see horizontal pretty well. Then I know where it balances. If the plan shows a balance point, balance it horizontally at that point and fly it. Or do your own calculations and fly it using a calculated point. Then you can test it in flight to see how you like the balance point.
I do think the term "tail heavy" causes confusion. I agree that if a plane is tail heavy it will be overly sensitive on elevator in a way that cannot be corrected simply by expo or reducing throw. "Tail heavy" means that the balance point is too close to the neutral point, or is behind the neutral point, which makes it difficult or impossible to control. If a plane is "nose heavy" it means the balance point is too far ahead of the neutral point. Then the plane will need a more negative stab angle to keep the nose up, which means power changes will have a bigger effect on trim, drag will be higher, and the plane will land hotter. However, at a give engine speed, it may feel comfortably "solid" because it will not be very sensitive to elevator.
My balance point on my N.17 is at the point shown on the plans, which also corresponds to the point I calculated. I balanced the plane at that point horizontally. The stab is packed with some washers at the leading edge where it screws on, so it is somewhat positive compared with the plan. It was adjusted that way by a previous owner long ago, and I found that it worked perfectly. It's nice to be able to make that stab adjustment. On most models the stab is fixed.
The problem with shimming the trailing edge of the wing instead of shimming the stab is that you change the downthrust. Downthrust depends ONLY on the relationship between the thrust line and the wing. If you have no downthrust and you shim the trailing edge of the wing, you now have up thrust. As noted above, it's not a good idea. That's why I think that if you need to trim the plane so it doesn't climb so much, and you can't change the stab angle, it's best to just leave in the elevator trim. Sometimes it works to raise the trailing edge of the wing, if there is already some downthrust, you might not lose enough to matter.
Jim