HH,
Exactly right, as that is how the game is played. Introduce the high figure as a hypothetical "worst case", thereby being able to deflect any direct challenge by reference to the fact that it is "only" hypothetical, then as the years roll by, refer to it in increasingly concrete terms as an estimate, budget, etc
By getting a big number out early into the ether it price conditions the customer, and of course, he who warns is forgiven....