Built-under oven and induction hob

I'm revamping the kitchen. New granite worktop 3cm thick, so the existing induction hob will project 2cm below it. I want to replace the existing single oven underneath it with a double oven 72 cm high, the same as the cupboard doors adjacent to it. I'd rather naively assumed that as the controls on the fascia of built-under ovens are at the top, and the actual oven therefore doesn't extend anywhere near the top, that there would be ample space for the hob above the oven.

But insofar as I can find installation instructions, this doesn't seem to be the case. The external top of most ovens is only a centimetre or two lower than the top of the fascia. When I tried to make this point in Currys, they look at me as if I'm an idiot, and say there isn't a problem. When we prise out the hob on one of their display units, and I point out that they have a 4cm laminate worktop, and I still don't think there's any gap for ventilation, they still look at me as if I'm an idiot, while edging slowly away.

Firstly, it would be nice to have confirmation that I'm not an idiot! Secondly, can anyone point me in the direction of a 72cm high double oven that does have space for a 5cm deep hob above it. And if not, how about an hob (induction or ceramic) that is only 3cm deep so it doesn't project below the worktop.

I'd be very grateful for any advice.

 

Possibly I am an idiot! Totally overlooking that the oven has to slide in below the top rail, so it's got to be a minimum of 18mm below the worktop. I was assuming that there had to be a bit of a gap for ventilation, and I hadn't got down as far as millimetres, but I suppose it might just be OK. Still seems awfully tight though.

 

http://www.thekitchenappliancestore.co.uk/product.php/22139/beko_ctf22309x
According to the Technical Diagram (click under the picture) the worktop over this oven must always be at least 38mm thick, or 50mm thick if you want to have an induction hob. News to my installer, I suspect, if this is generally true.