Joel, My reasoning for three hooks is this, Two hooks one at each end will spread the tension on any one point. Why not use two points to lift a load, lifting 1000 lb will put 500 lb on each hook, spreading the load.. Also, if you are in a narrow space, then the hooks on the end will have the advantage.
Another thing to everyone, why are a lot of hooks welded on with the open side to the rear? Do you really want your chain to ride on the lip of the bucket? Lifting maximum load might bend the lip.. You will be able to lift more if the chains were on the back of the bucket, and the fulcrum point will be right over the hinge part of the bucket, and you can still curl forward.
Now with all that said, about the only advantage I see with the chain crossing the lip of the bucket, is that you can also use the curl cylinder, for a little more height. The bucket bottom is usually longer than the back of the bucket.. It would depend on the size of the cylinder whether the curl cylinder has equal, less or more lifting force, you have to understand that the push force is always greater than the puilling force.. I think a single hook in the middle with out a backing plate is not a good idea. Perhaps Two hooks on each end of the bucket with one of the hooks facing forward, and one facing to the back of the bucket. I also think the receiver assembly mounted is a good idea, because of it's versatility with the many attachments that one can use.