If you look at the Modern-Aire site, they have several shapes where the front tapers at the top to the depth of an upper cabinet, and the sides are straight so as to butt up to, and cover, the yellow cabinet sides you mentioned. Their typical sizes are 18" and 30" high, but you could get a 24" custom one if your budget allows. Or you could get an 18" and have a box made for above it to cover that area and to which you could attach replacement moulding. The box could be made of either wood matching your moulding or sheetrock. Vent-a-hood has a stainless direct replacement if you decide to stick with the same size you now have. I'm attaching the link to the Modern-Aire page that shows their shapes. PS-10, PS-11, and PS-26 all have the characteristics I was talking about above. Here is a link that might be useful: Modern-Aire Hoods

Stainless steel easier to wipe down than wood. Also, it’s more of a pain to buy the separate components for a hood with cabinetry surround than a metal hood where it comes all-in-one. Also you need to make sure that the cabinetry surround is designed with proper proportions. A metal hood, you just shop for the one with the correct measurements. For a cabinet hood surround, you will have to carefully examine what the designer‘s hood surround plans are. It needs to be 6” wider than the cooktop. It must be deep enough front-to-back which is at least 24” deep; a common error of cabinet hood surrounds is that they are designed too shallow. Also sometimes a cabinetry surround plus a wall of more upper cabinets all around it can look like too much wall of cabinetry. Depends on the design.

Hi there! While it isn't the most common, there have been times we have made a very long/large range hood and only need a certain size insert (for example 10' wide hood, only needing a 48" liner), so most often what we would do is install a stainless steel panel to allow everything to look smooth and coherent with the liner. Some people opt to add lighting to the "dead" panel space, and I would definitely recommend making sure you get the proper CFM for your space, but yes you can have an insert smaller than the range hood. Hope this helps!

When there are cabinets providing partial side skirting to the hood, in that area the hood is effectively wider, or at least collects the expanding and constrained by the cabinets plume effluent. Front burner pans, however, can generate plumes that will escape when not overlapped by the hood capture aperture. More CFM will only partially help. Flow patterns presented in the ASHRAE Handbook show that the velocity of the hood air rapidly drops with distance down and to the sides, so effective hood size is only slightly wider than with a lower CFM. This already assumes that the actual CFM is that which is needed for a given plume upward velocity -- perhaps 2/3 of the blower rated CFM divided by the hood aperture area.