Grace56
The Decision Letter should explain how the Decision was made you can also ask for a copy of the PA4 Assessment report by contacting the DWP.
As to whether you should ask for a Mandatory Reconsideration, only you can decide this but if none of your limitations have changed then it does beg the question as to why the award has been reduced.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems