How the basic pay is fixed for a retired reemployed pensioner?

I retired from University as professor. I am currently reemployed as Special Secretary with a pay scale of 75500-80000. From my monthly emoluments a sum of Rs 19000 is deducted which includes pension, allowances, commutation. The audit is of the view that my BASIC pay as retired reemployed pensioner should be fixed ata a level lower than the pay scale by deducting the pension basic from my present basic. Thus, they refix my basic pay as 75500- 22500 (my basic pay at the time of retirement)= 53000.

Is this correct/ How can my new basic be below the minimum of the present scale? What are the rules regarding basic fixation? I was advised by a consultant that the right way to do this is to allow the present scale and allowances and DEDUCT the amount I receive as Pension, commutationand allowances fromt the gross salary received.

Which is correct? How can my basic be below the lowest of the pay scale. How are other allowances calculated?