Every bit of the wood underneath needs to be covered with stainless. Then center the aperture over the cooking portion.

Just make sure you can reach the controls OK. You don't want to catch your clothes on fire if set too far back.

Thanks for your response. All wood will be covered with stainless. The controls are at the front so it shouldn’t be hard to reach, wherever it is placed.

I just wanted to make sure I get proper ventilation, especially at the front, where we do most cooking. I wasn’t sure if the manufacturer’s design the units assuming that they will be flush with the backsplash.

As Zumi wrote, generally one wants the hood centered over the cooking zone (locus of possible pan edges). In some circumstances, such as when there are side curtains or cabinets, a bit more forward alignment may improve capture of the front burners, with the back burners' capture aided by the cabinets.