Just as one wants some volume below the baffles to aid averaging transient cooking plumes over the baffle space (helps avoid plume spillage), so too does some volume above the baffles help keep the flow uniform across the baffle space aiding filter function. Narrow hoods may have poor uniformity of flow unless the filter is somewhat restrictive, and lo and behold, mesh filters fill that bill, particularly once they have picked up some lint and grease. One doesn't want the filter to be restrictive more than necessary for filtering, because pressure loss causes blower flow rate to drop.

Over islands, the best performance hood that can be fitted and afforded is needed due to the general preference for increased hood base height for sight line clearance, and due to the presence of cross drafts that move the cooking plume horizontally at the hood entry aperture.

Cooking effluent has momentum. Think of water sprayed upward. Wherever the water hits metal it splashes. One does not want the splash to escape the hood, either by missing it on the way up or bouncing out because the entrainment air flow is too weak.