Hi Vausian I have been a kitchen designer for more than 20 years and most of the kitchens we do are quite large and therefor often have an island. So we are very used to kitchens with hobs in islands and the importance of good extraction in this situation. The only solution we have recommended for the past 4 or 5 years is 'cooktop extraction' from Bora. They uniquely look at the hob and extraction system 'as one' and make the best extraction systems by far. They are also very discrete, relatively simple to design into a kitchen and install. Please have a look at their website to see the 3 different levels of their range, Basic, Classic and Professional. https://www.bora.com/en/ CK

Unless you like to cook a lot of fry-up's I think a fairly powerful extractor fan should still be effective even when set back a bit. If you really want to position it over the hob you could have a contractor build in a robust boxed in false wall onto which you could have a normal 60 or 50cm wide extractor hood mounted. It would have to be anchored well to support the weight, the electrician would need to allow more power cable and a longer flue but it shouldn't be all that expensive or difficult to do. You'd probably want to make the cupboard next to it an open one or check carefully that the door is still functional.

A Bora extractor is often acknowledged as being the quietest more efficient extractor because it extracts at pan level. This will challenge your budget but you will get the hob included too. Alternatively look at any extractor with an external motor- again these will challenge the budget but as the fan is normally outside it is also quiet.

Neffs own website has the answer. This extractor (like pretty much every other modern extractor on the market) requires a 6” ducting. A 4” duct allows less than half the extraction this hob is capable of (think trying to breath through a drinking straw). Get the builder to do it properly rather than what’s easier for him.