Hi, I think brass will be fine. I'd go at least as wide as the inside of the surround.

Ah, looks like your first picture is missing.

With any electric hob its recommended to have a wider extractor than your hob top, even more so with an induction hob and 1.5 times is about right have a look at https://www.neutratest.com/en/cooker-hood-guide/need-to-know-about-cooker-hoods/width other consideration is that the motor is powerful enough for about 10 air exchanges per hour according to the room size https://www.neutratest.com/en/cooker-hood-guide/need-to-know-about-cooker-hoods/extraction also helps if you turn the extractor on when you start your prep work and before you actually do any cooking so the air movement in the room is already being drawn towards the extractor.

Have you tried living with it and if so does it work or can you see that steam [for example] escaping up the sides of the extractor. Ideally this extractor would be ducted to outside, if its in recirculating mode than you're going to struggle as all it does is 'clean' the air and having it at 1100 wide may make minimal difference. The power of the extractor to the size of the room is also very important, ideally the maximum extraction rate of the appliance should be 10x the volume of your room. Also there's lots of contemporary extractors on the market today which aren't shaped to match the footprint of the hob below, some are cylindrical tubes and others look like glorified light fittings so having a matching extractor to the hob below isn't always a customers requirement if they prefer a particular look/design. To use the extractor properly, ideally turn the extractor on when you start to prep your food, so then the air in the room will be circulating towards the extractor when you start cooking. Having a gas hob helps as this is considered a 'hot' heat [electric hobs are 'cool' heat] as the effect of the gas flames warms the air so you have columns of rising warm air around the cooking steam and smells so it doesn't fan out as it rises, so in practice you may 'get away with it'. Bear in mind with most extractors, having a wider version doesn't mean that the motor is any wider inside the extractor and a lot of them may be only the glass surround is wider for a 1000 wide to a 600 wide unit for example. As Isla stated, unfortunately in the suppliers terms and conditions the onus would be upon you to make sure that everything is suitable even though your kitchen supplier has supplied the appliances, which does seem unfair as you the customer is not a professional and a lot of what you see in a listing is a load of codes and shorthand descriptions. If you purchased from a local independant than possibly you mentioning that you find their service very disappointing and that you will be leaving a negative review may help, but if you've purchased from a national like wren, then they will just say 'you signed' and couldn't give a f$£% if you leave a bad review.