Triskele
I am afraid that this is the policy of the DWP, the move from ESA(CB) to ESA(IR) is treated as a normal Change of Circumstances and as a result, the ESA(IR) is calculated from scratch with no reference to either the proceeding ESA(CB) payments or the IB payments before that.
As far as I can tell, the legal side of it is that the change is done under the ESA Regulations 2008 which do not contain any Transitional Protection clauses, as opposed to the ESA Transitional Regulations 2010 which do.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems