A recent session saw us—the PCs—encounter a gate made of magical fire. The wall surrounding the gate was 30 ft. tall.
When the Oath of the Crown paladin and I were on one side of the gate, the paladin used on an enemy creature his champion challenge Channel Divinity option that says that the affected creature can't willingly move more than 30 ft. away from the paladin. Then my PC knocked the flying creature through the fire.
The DM tried to have the enemy creature fly over the fire to avoid having it go back through the fire, but I said that since up was more than 30 ft. away from the paladin the enemy creature couldn't fly that way.
The DM reluctantly agreed, but now I'm wondering who was right.
Should effects like champion challenge be considered spheres or planes?