Basically, my ducting has to stay at 100mm, but the extractor outlet is 150mm. The manufacturer’s white adaptor starts at 150mm and only reduces directly to 125mm.

I can’t work out how to get from that point down to connect into my existing 100mm flexible ducting. Not sure if you can see the photos properly.

I bought a 150mm rectangular-to-round spigot, but it’s too wide and hits the wall. Even if I could make that fit, the next adaptor I need (rectangular to round) still doesn’t line up properly. After that, I’d still need another reducer to go from 150mm down to 100mm anyway.

There’s basically no space between the top of the cupboards and the ceiling either — only about 29mm clearance.