I would expect that for those whom it works, it calms inflammation. That would allow an enlarged organ to reduce, but I would not expect a normal organ to be shrunken below normal parameters.
I'm not sure it's any more risky to play with dosing of Pygeum than it is to play with dosing of Dairy Queen soft serve. Have a small, have a large, have it 1x a season or 1x a week, or 1x a day. Too much sugar will cause you issues, but it will take time for the damage to present. If you listen to your body, keep your Dr. in the loop ("are you taking any medicines or vitamins?") & get your physicals in a routine manner - you should have awareness of benefits or detriments in a timely manner when things are reversible if desired.