I think I know exactly what you're talking about. I have a feeling this is a Honda 'safety' feature. I had a 92 Mustang 5.0 which I could put into 1st at say 80 km/h... handy when coming up to a stop sign, knowing that you've got to stop, and will be taking off again in 1st (albeit probably not the smartest idea should your foot slip off the clutch). I basically had to re-learn how to drive the Honda tranny; like you say, "If im going below like 20 or 30 it seems to downshift fine." That's normal... you simply can't put it into 1st below say 30 mph (40 ish km/h).
Don't force it... if you find youself having to force things, you're doing something wrong.
I agree with this:
Also, why are you downshifting? IMHO, save on transmission wear and use your brakes to slow the car. That's what they're made for. I would only downshift when you are in a race environment, autocross or road racing.