Hmm...I looked back at the original declaration, and I think you have a point.
a) Both wizard contingencies trigger at the same time.
b) The sorc's contingency triggers after the Dispel Magic.
c) Therefore, even if the other wizard had DD'd to the ground, no matter where he landed, the Sorc could have DD'd somewhere not within 60' of the Yuan-Ti.
d) In other words, regardless of initial position, the Sorc is able to DD more than 60' away from the other Yuan-Ti.
Therefore, this is my final ruling:
1. The sorc did fail his Crown of Madness save.
2. There is a Yuan-Ti close to the ground, regardless of how far he moved, he is not adjacent to the sorcerer.
3. All mounts are high in the sky, as they do not fit through a Dimension Door.
4. To simply end haggling over distances and how far who moved when, I rule the Yuan-Ti on the ground is 100' away, and the Yuan-Ti who is falling is, as earlier stated, 150' from the ground, and, when he lands, will be 300' away from where the Sorc is now.
The sorcerer may act normally on this turn, though he is charmed by the Yuan-Ti who cast Crown of Madness on him and may not take hostile actions against him. I include in this ordering his Simulacrum to attack this particular Yuan-Ti.
It is now the Sorcerer's turn. bangs gavel