MUA may be introduced to the kitchen in any way that doesn't cause cross-draft disruption of the rising expanding cooking plume, but not in any way that "short circuits" the ventilation by flowing into the hood in place of the plume. A diffuser in the ceiling next to the hood might violate both aspects unless the diffuser blades were oriented to force the air away from the hood along the ceiling such that the air current would follow the ceiling, wall, and floor, ultimately approaching the hood from below. There is no limit to how far away the MUA is introduced so long as there is a path to the kitchen air volume. Devious paths may require consideration of their pressure losses when analyzing the MUA performance. As for hood overlap, the principle that is being addressed is that the cooking plume (with gas jet plume where applicable) rises and expands from a hot cooking surface (and from around it when gas cooking). The plume velocity profile (and effluent per unit time profile) is mountain shaped, but the larger part is contained roughly within a 20-degree cone. (Plume shapes vary with temperature and cooking surface.) The cone half angle, then, is 10 degrees. So long as the hood collecting aperture is at least 10 degrees outside every effluent emitting point on whatever pans you use, you should obtain decent capture, barring cross drafts. Note that at 36 inches above the pans, 10 degrees is an offset of 6.45 inches. This is as I said from the pan bases (pan edges for gas flames) and not from the edge of the cooking appliance. Where this doesn't apply is at a back wall where present, and at the sides if cabinets or side skirts direct the plume upward. The hood effective aperture also grows slightly with air flow into the hood, but this is likely (at the recommended 90 ft/min) to be only a couple of inches added effective capture area. The exact behavior depends on the velocity profile of the plume vs. the velocity profile of the hood intake at the edge. (Figure 6 page 30.4 of the 2003 ASHRAE HVAC Applications Handbook provides an illustration of how quickly the hood air velocity drops past the edge.) kas

For dc applications, one might think of capacitors as having some battery like properties -- generally less amp-hr capacity than a battery, but lower series resistance. In ac applications, a capacitor (left to itself) provides a 90-degree phase shift to the relationship of current vs. voltage. In EE terminology, the relationship of voltage to current is the impedance, and passive ideal components are characterized as: resistors (Z = R), inductors (Z = wLj) and capacitors (Z = 1/wCj) where Z is impedance, w is natural frequency (2pi f) and j represents the square root of minus one; R, L, and C are resistance, inductance, and capacitance, respectively. The use of imaginary numbers relates to the imaginary exponential definitions of sine and cosine, or alternatively, the use of vectors in the complex plane to represent phase and magnitude. Combinations of these components can provide various frequency dependent voltage vs. current functions. Even more potential for voltage vs. current functions exist when the components are used within active circuits. In other words, even the most basic aspect of electrical engineering is more esoteric than one might imagine. In the motor circuit, the purpose is merely (!) to shift phase. I expect that capacitors have been performing this function since before vacuum tubes were developed for amplification in radios. Large single phase motors not needing capacitors were used a century ago, e.g., induction repulsion type, but I think they have fallen out of favor, or are only used where the capacitors would need to be monstrous. Most industrial areas of the US have three phase power these days, so capacitors are not needed for large motors because the three phases already provide the necessary phase shift. Tiny synchronous motors as used in clocks directly wired to electricity use a different no-capacitor technique to shift phase -- I think I've seen a description somewhere on the Internet. kas

Let me say this about the premise: The specific flow rate that is needed (CFM/sq. ft. of hood aperture) for good containment of whatever is captured by the hood aperture mainly depends on the rising cooking plume velocity at the hood aperture, with minor effects from various factors related to the hood design. The plume velocity depends on the temperature of the pan base, but with gas cooking it is augmented by the entrained combustion gasses passing around the pan. Hence, for the same cooking temperature, induction should have a lower velocity plume than for gas cooking. The "Finnish" experiments I've referenced in the past show this difference in peak plume velocity. Electric coil cooking might be expected to be intermediate, as some coil heat escapes around the pan edges. A 3 ft x 2 ft hood would require a blower that was rated at 600 CFM over induction to meet this requirement (900 CFM for gas). If the hood is undersized, and/or the cooking limited to lower temperature cooking than searing or wokking, then the hood CFM can be commensurately smaller. To avoid MUA system cost, you may wish to find the no-supplemental-MUA CFM limit for your code enforcement area and go with that. I would still try to make the hood wider than the cooking zone to improve capture, even if the specific flow rate drops as a result.

I can't comment on those specific models, but we had a Zephyr Monsoon II model AK9346AS installed about a year ago and it we found it to be impossibly loud. Their literature says the sone level on low is 3.5, which, based on this chart, is about 45 decibels. I downloaded a decibel meter to my phone and with the phone sitting on the stove 35 inches below, the noise registered 80-82 db. That's MUCH louder than advertised, and we found it very uncomfortable and annoying--couldn't hear the Sonos speaker 12 feet away or anyone talking in a normal voice, and there was a sigh of relief whenever we turned the fan off. We eventually decided to switch it out and install a Wolf liner (with variable speed knob), an inline silencer, and 1400 cfm Abbaka roof mounted blower. It's quieter on high than the Zephyr was on low. The three pieces are a more expensive proposition (even if we hadn't made the Zephyr mistake), but the result is so vastly more pleasant that I still smile when I turn on the fan. In a nutshell, if there's any way you can listen to the Zephyr and Best, preferably in a similar setting, do it. Don't trust the literature.