The take-off/neutral setting is an arbitrary reference point. Arbitrary in that the flight crew don't necessarily know whether it causes the tailplane to provide a downforce or an upforce.
An a/c can be stable with an upforce type tailplane as with a 'conventional' downforce type tailplane. Think of 'tandem wing' designs.
Without data from the manufacturer, how is a pilot supposed to know? All we can know is that for a given CG position then the trim should be set to 'x' [b]units[/i] with 'x' units providing adequate control authority/control pressure for that condition of flight.
The obverse of this is that if the control pressure is relieved then the trim is providing an appropriate amount of 'alternate' pressure for the condition.
This still doesn't inform about whether a tailplane is an 'upload' or 'download' design, only that there isn't a control force required from the pilot.
The designer decides where 'neutral' is, and what the mainplane/CG/tailplane relationship is.