Chadaudio-the mistake you may be making (if you are making a mistake, you may not be) is in the mastering of the American CD.
Are you sure that one is the remastering done by Page because these were not issued singular fashion until a while after the grey box set.
If you are sure of that fact then you will be right the Jap versions are better.
It is possible the Jap versions are better but I was led to believe like the Pink Floyd mini-LP versions these discs were only repackaged from the most recent remasters.