You answered incorrectly, it is correct to put the two Warehouses on top 100% of the time in the situation I explained (occasionally it is a tie if your deck is all silver, but in a deck that is some generic heterogenous mix of Silver, Gold, and Copper, it is not a tie, and in a deck that is a generic heterogenous mix of a Smithy Village (woodcutter?) Engine it is not a tie.)
This is kingdom insensitive, it requires a strange puzzle solution for topdecking the Dungeon to be correct, something as forced as Menagerie being part of your deck's design, or being trashed down to seven cards, or wanting Courtier to hit Dungeon before you play it.
You are failing to consider that you are being offered the opportunity to discard one Warehouse to the other and accept a 4 card hand, the same four card hand that is your only choice when you choose the Dungeon. However, if after drawing three but before discarding, you realize that you cannot hit the pricepoint you desire unless you "go big or go home" and hit some golds, you have the option to go after that three card hand. But the four card hand is always available to you.