Phil
I suspect that the issue isn't whether or not the nosewheel is on the centreline, the issue is whether the nosewheel is on the centreline and the fuselage is aligned with the lead-in line..
I have found that even being on one side of the line, the system might have me turn away from the lead-in line in order to get the aircraft centre-line aligned with the parking. When the system tells me to turn in a opposite direction to what I am expecting, it is usually shortly followed by a turn in the original direction I was expecting.
It is a very sensitive system.