I would look at the Vent-A-Hood KH34 liner/insert. The dimensions look like it would fit in the cabinet opening and not require any fillers in the bottom of your cabinet. The one from Home Depot looks like it is very shallow and will require fillers on the front, back or both.

https://ventahood.com/index.php/support/specifications?id=361&view=article&model=KH34SLD

Replace the uselessly shallow cabinet hood instead. It's a well known issue that nothing really fits it, and it isn't deep enough to work anyway. Pick an accent wood or color, or metal, and have your carpenter make something.

Try selling the insert on eBay. You won't get back $900, but at least something, if it is new and unused.

Your tale is why I dislike cabinet hood surrounds. This kind of thing happens all the time with them. And the cabinet hood surrounds are never deep enough to cover the cooktop properly. I know it's not what you want to hear, but perhaps consider ditching the cabinet hood surround and buy a stainless steel exhaust hood. I am sorry that I don't have additional advice. Like I said, cabinet hood surrounds can be problematic and finicky.

😩😩😩 this is exactly the responses I was dreading but I know this might be the only way to go. I’m hoping the new one I ordered will fit. The CFM on the old one is barely covering any exhaust but at this point I just can’t justify spending more money on this. I’m hoping my contractor will find ways to fill this out and make this new one fit.

I feel like my only choice would be like someone said above — get a carpenter to custom make a hood cover for me so that we can end up using our original insert. Maybe down the road when we save up more. This reno already took so much out of us. Ugh.

Thank you everyone!

CFM on the new one*

The old insert CFM is 680. This new one is only 380 😑

Did you buy the Cosmo? Do you like it?