How do you mark an answer as an educated guess. Ah well, perhaps this will help.
Different points on the earth's surface must be at different distances from the moon. The angular diameter of the moon is greater at the point on the earth that is closest to the moon (nearer things are bigger). Is the greatest eclipse at this place?
The transit time will also be impacted by the rotation of the earth, which will have the effect of shortening it as the moon takes aprox a month to get round and the earth surface only a day. In the location of the "greatest" eclipse where the surface of the earth intersects the shadow tangentially the rotation is in the most effective direction for a rapid transit. The longest transit time must be elsewhere; where the angular diameter of the moon is nearly largest, and the surface of the earth is cutting a slightly longer section through the shadow.
TBH It's an enhancement to the question, I suppose, given that I have been creative.