Is it really necessary for a range hood to extend out from the wall completely over the burners? Doesn't it draw from a wider range than its footprint? There must be objective studies about this. If they had to be wide, why does a reputable brand (I think) like XO make hoods that are less than 20 inches deep?
The deeper the better; ideally, it should be as deep as the range. Closer to the burners is better too, as is a higher airflow, within reason. Beyond 300 CFM, you might need a makeup air system or to be diligent about opening a window when it's running.
I couldn't find anything in International Residential Code that specifies range hood size, so it would appear that size is more of a style choice. Table M1507.4 does say that the minimum exhaust rate of the hood must be 100 CFM intermittent, or 25 CFM continuous.
Section M1503.4 of the IRC says that if the exhaust hood exhausts 400 CFM or more, then you must provide makeup air at the same rate. It also says that the makeup air system shall provide a means of closure, and must automatically and simultaneously operate with the exhaust system.