My Chinese blue fir is also about 20 years old and is 25ft tall or so (I have a two story home and it is considerably taller than the house). I know of a dwarf cultivar called 'Little Leo' - I wonder if your plant is Little Leo to explain why yours is shrub sized and mine is a towering tree.
I am including a link to the data base regarding Little Leo but there haven't been any pictures posted to its entry yet.
Hayta Tree (Cunninghamia konishii 'Little Leo')
