My island hood is 34 inches above the cooktop surface. Size that matters is the internal aperture, which is 27 inches front to back. This is centered over the boundary of the hob diameters. Width is the largest that Wolf supplied at the time, and covers with some overlap both an induction wok hob as well as a 36-inch wide induction cooktop. Fan is nominally 1500 cfm. Actual flow at minimum house negative pressure (i.e., with MUA) should be around 900 cfm due to baffle, transition, and duct losses vs. the fan curve. Capture is nearly complete in most cases.
When the aperture is moved up to seven feet above the floor, a hood is in the commercial installation category, and flow rate per square foot of aperture, as well as overhang beyond the cooktop zone, should also be commensurate with commercial practices. Twenty inches of pan edge overlap on each of the four sides is recommended for island configurations. (More exactly, the angle between the hood aperture edge and the nearest pan edge should be at least 22.5 degrees to vertical.) With a wall backing, and side cabinets, reduction is possible in those directions. The Greenheck reference material at my Clippings can provide more perspective, and the thermal plumes analysis papers more details.
For baffled hoods, aperture area (sq. ft.) times 1.5 ft/s times 60 s/min is the lowest air flow full-power achievable capability that I would recommend. This assumes that the baffles provide an effective factor of two air entrainment velocity enhancement to the impinging effluent. (The effluent rises from the pan at about 3 ft/s.)
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