That's a house rule of mine. At least the way we play is is that one side of the large beast's body is the starting point and we count from there. When the counting stops, or are interrupted, if able, that beast's head goes into that space and expands back from point of origin. The only time a monster could expand into a space further then that was if the beast could not fit into a space otherwise. This gives the OL something else to think about when plotting moves and keeps slow beasts slow and smaller, faster beasts, fast.
Be aware that the game was designed with monsters getting at least that extra move (large monsters all have very low speed values to accommodate for that). The above "house ruling" that FFG was considering isn't to reduce large monsters' movements for most of the time, but to help eliminate some of the confusion that happens when a monster can interrupt its movement (even if it's just after declaring the move action, but not having moved any spaces, which is currently legal), expand, perform an action, then re-shrink, finish moving, and re-expand gaining even MORE movement than before.
Example (as I understand things): A Hero is 3 spaces away from a dragon. OL wants the dragon to attack and move away.
Example w/ current rules: Dragon declares a move action, shrinks to a space 3 spaces from the hero, interrupts the move action by declaring an attack against the hero, expands in the other direction (essentially pivoting for no movement, doesn't count as entering a space next to the hero, so doesn't trigger certain hero abilities), so it is now adjacent to the hero, makes the attack, re-shrinks to its original position, moves away from the hero, and re-expands away from the hero, now placing it 6 spaces away from the hero.
Example w/ possible change: Dragon declares a move action, shrinks to a space 3 spaces from the hero, doesn't have the option to expand upon interrupting, moves 2 spaces to be adjacent (possibly triggering hero abilities), makes the attack, finishes moving one space back toward where it came, expands, and is now only 2 spaces away from the hero.
Another option is that you still allow/require expansion, but when you declare the action, it must be able to be performed from your current space (before expanding) instead of just being possible when you expand
Using our example: Dragon declares a move action, shrinks to a space 3 spaces away from the hero, moves 2 spaces to be adjacent (possibly triggering hero abilities), makes the attack, shrinks to the space farthest from the hero, finishes moving 1 space, expands away from the hero, and is now 4 spaces away from the hero.
(These figures become slightly less extreme with 1x2 or 2x2 monsters)
Actually, re-reading my examples and the FAQ, it may be the last example that they use (forcing large monsters to be able to re-expand, but that they must be able to declare the action FROM THE SPACE THEY ENTERED before interrupting movement) And may be how I house-rule things if I do.