The use of the "4-6 feet" reference is a holdover from the days of error-counting, the same notion also permits the idea that you can cycle back and forth between 4.1 and 5.9 feet in a sine wave and that is "not an error" which is definitely not true.
Brett
This is a good conversation. I decided to look at the 2024-2025 rule book online.
This is from the "Judges Guide"
14.5.1.
Recognition of level flight altitude of 1.5 meters (4.9 feet),
plus/minus 30 cm (1 foot)
Doesn't say anything from the center of the circle in that section??
On the maneuver descriptions by which the scores are derived from it says, for example..
Takeoff.
A correct takeoff consists of the
model rolling smoothly along the
ground for a distance of not less than
4.5 meters (14.8 feet), but not greater
than one quarter of a lap. The model
then rises smoothly into the air with a
gradual climb and a smooth level-off
to normal flight level over the point at
which the model commenced its
ground roll. The model continues on
for two (2) smooth laps of normal
level flight to point of original level-
off.
Maximum 40 points. Minimum 10 points.
Errors: The model bounces or becomes airborne too soon, or too late.
Takeoff, climb or level-off is not gradual and is not smooth. Level-off
occurs too soon, or too late. Level-off and normal flight level are not
within a height of 1.2—1.8 meters (3.9—5.9 feet).
Also the drawings, which are aids, show the normal level flight to be looked at on the path of the model and not from the pilot. I can see why this has been a point of discussion for many years.

While 4-6 may be a hold over from the old days 3.9-5.9 is everywhere in the rules right now. It would appear that as the pilot on each maneuver you have that area to work within and still be in the rule book. That doesn't mean hunting all around within that range. I would think it to mean if I set the bottom of my first maneuver 3.9' the rest of them need to be there for the best score possible on that portion of the maneuver. Then on the next maneuver once again I have all of the 3.9-5.9 work with until the entry point where the height is indeed set by me...