The key point is not an arbitrary 1/2”-above-the-soundboard for neck set.
Instead, it’s the relationship between the plane of the fingerboard and the front edge of the bridge. Even for Martin, bridges come in different heights, and they set for the height of the front of the bridge, not an arbitrary 1/2” measurement.
The 1/2” measurement is between the strings and the soundboard, and is considered an ideal to shoot for when the instrument meets the following criteria:
- The plane of the fingerboard intersects the top of the bridge
- There is a saddle installed in the bridge
- The instrument is strung up and the strings pass over the saddle.
That’s when you’d ideally see about a half inch under the strings - but it can vary a bit either way, as long as the overall geometry is right.
OP is conflating an ideal setting for the full bridge-and-saddle height of the strings above the top with the neck set - the two are not the same.
As other wiser builders have noted, an overset neck (where the plane of the fingerboard overshoots the front of the bridge) is a recipe for putting too much stress on the saddle and risks breaking out the front of the bridge. Fixing it requires either resetting the neck to the plane-of-fingerboard-intersects-bridge-top geometry or a very, very thick bridge.