ccache ignores CCACHE_DIR

Question

I have two identical projects with the same file

/Users/Steve/Desktop/foo/a.cpp
/Users/Steve/Desktop/bar/a.cpp

I use ccache to speedup the compilation across directory boundaries, so I defined CCACHE_BASEDIR

export CCACHE_BASEDIR=/Users/Steve/Desktop/

I compile the file with the following command:

export CCACHE_NOHASHDIR=true
export CCACHE_BASEDIR=/Users/Steve/Desktop
ccache clang++ -c /Users/Steve/Desktop/foo/a.cpp
ccache clang++ -c /Users/Steve/Desktop/bar/a.cpp

Is there any reason why the object file for bar/a.cpp doesn't get pulled from the cache?