Volume below the baffles helps average hot plumes over more baffles, thereby making the required CFM less in some (!) conditions. The tented design, as in my Wolf Pro Island hood shown below, is very modest in volume, so my opinion is that the flow rate should be based on baffle gap air entrainment velocity requirements and not depend on much averaging. Commercial hoods with deliberately large reservoirs below the baffles can make full use of the volume for averaging the plume(s) over the entire baffle space (typically only one sided).

Tilted baffles tend to move grease to the lower ends, but how important this is depends on how much greasy stuff one cooks.

Subtleties of air flow can allow or not having physical hood boundaries larger than the baffle space but yet include it all in the effective capture area. For the 1-inch-ish edges of my hood, the air flow is sufficient to count that area, in my opinion. The light bar is probably only partially fully efficient, so I don't usually count it. Baffle frames, holders, etc. that are inside the boundary will not reflect plume portions out of the hood if the flow rate is sufficient.

Testing this requires either schlieren photography or heating high smoke point oil (e.g., peanut oil) until it smokes and observing how much is not captured.

(click to enlarge)

Thanks for the information. It sounds like your take is that a hood like the Zephyr Titan is likely to have better capture than the Zephyr Sienna Pro and require less CFM (comparitavely). And that I would not practically want to consider something flat like this Best Range Hood with deeper lighting bars. I like the depth and thin edge on the Titan... too bad they do not make it in a 54"!

We don't cook many meals with high grease... we may wok or fry occasionally, but not regular.

The goal for residential hoods with baffles is to entrain the plume components into the baffle slot flow. Two hoods with the same entry aperture, but different reservoir volumes may have slightly different thresholds of plume spillage CFM requirements, but I would design for 90 ft/min across the aperture, and not try to account for minimal added averaging that the tented baffles configuration might provide. 90 ft/min == 90 CFM/sq. ft. Don't forget the added blower rating needed to get this flow in the presence of pressure loss from the baffles, ducting, and imperfect MUA. Maybe 1.5X.

Thanks. Luckily, in my case, the blower losses due to ducting should be on the light end. Basically 2' up from the ceiling and out the roof, with one 20 degree bend.