Flying monsters in units

So I was reading on another forum about characters on flying mounts joining units. They still can't join flying units but they can join other units. However, I believe if they do they have to use their ground movement characteristic.

pg 13 of the BRB in the section: MOVING YOUR UNITS second paragraph last sentence;
"If, for whatever reason, there is more than one Move characteristic in the unit, then the entire unit is treated as having the same move value as the slowest model."

with that in mind

pg 70 section: FLY, subsection: MOVING FLYERS second paragraph.
"Units made up entirely of models that can fly can move or charge normally on the ground, using their movement value, or instead choose to fly."

the unit is not made up entirely of flyers, thus they have to all move/charge on the ground ... using the lowest move characteristic. That would mean that a chaos sorcerer on a disc will force his unit to move at his ground movement speed of 1" or an eagle-rider would force his unit to move 2".

Probably not something that will come up that often, but I thought it was interesting.

I had no idea that flyer's could join units. Its not something that will come up to often though.