Retrofitting ducting to a jumbo box

Has anyone got any experience of fitting that ducting that sends fan air to the rear of a Mk2 Octavia?

I have attempted this today but the ducting isn't quite aligning and I think it's due to the way I bolted the front section of the ducting down.

I removed the bolt in front of the handbrake, put the duct over the stud and then replaced the bolt. But, as a result, I think the ducting is sitting too low.

Appreciate it's a very niche question but, if anyone has done it, I'd appreciate your help!