Front Ventilation ducts?

It seems to depend on the type of duct ... Mine came from the uk and the only way I could fit it was to just keep massaging it to fit until it did but it still would foul the windscreen motor arm .... I then gently pressed it down at that point until it was quite compressed and then added some reinforcement and glue to keep that compressed state ...it's very hard but can be done

 

Is the problem the interference of the fan casing edge where the hose slips over
or
the fact the hose must make a very tight 90 degree bend?

I used the DinoParts corrugated hose and had no fit problems on teh edges so I'll bet you mean the latter as I had the same problem. Funny though, I found the Driver's side 90 degree bend to be a harder task than the poassenger's side - a much tighter bend. Anyhow, Try fastening the hose before you completely mount the fan or ventilation block. If needed, loosely spin one fastener.
Sounds completely backward but so many tasks are like that on the Dino.