Be careful! The post in the 1' hole will move relative to the other posts when it freezes, It will go up while the others will not move. Since frost heave can move an inch or more easily, this could really trash your deck.
You really have two choices: frost line or floating slab. If you put all of the posts down below the frost line, they should all remain stable. If you build a slab strong and thick enough (see building codes), it will move as a unit when it freezes. You can't mix the two!