The extractors don't come out quite as far as your work top underneath, (ours is 150mm set back) so you shouldn't be banging your head on it as you're not technically below it. I'm 5ft 11' and my husband is 6ft 3', our extractor is exactly 80cm above the hob. We don't bang our heads on ours.

I think if you put it any higher it will look weird.

I had the same dilemma a few months back. I had new kitchen put in along with new extractor. it was at height of 70cm above gas hob. the extractor come out 50cm.

I spent a few days trying to get used to it but in the end I was not happy and got the fitters back to raise it to 90cm.

it looks a lot better and reduces the risk of me banging my head off the side of the extractor!.

no problems extracting steam at that height. Glad I got it done as it would have annoyed me otherwise.

We have measured it all out and it really needs to be at 110 as my wife is tall 100 would be a min really but we don't want the extractor to be useless as long as it works we are happy with the look

Mine is 850 above the hob and I bang my head on it about once a month and I don't use the cooker every day. I was worried about how effectively it would suck the steam if it was any higher, but most of the time we have it on it's lowest setting which seems to be enough.

I can't see it being a problem, just turn the extractor on well before you start cooking so the air in the room is naturally flowing up to the extractor and as its a gas hob there's naturally more hot air rising so the steam will easily rise. Just size the extractor according to your room size as you're looking for 10 exchanges of air per hour. Assuming its being ducted out without to many bends/distance and in correct size duct.

As Lifestyle Kitchen says.

But why not a headroom hood or a (boxed in) ceiling unit? Costs?

https://www.novy.co.uk/products/cooker-hoods/wall-mounted/vision/7831/