Your point is right but it would be good if the RSA is done for trains moving within the same zone or almost equal distances just like : Chennai-TVC/Allp-MAS or Maveli/Malabar or West Coast/MAS Mail.
In case of Cheran and SBC-MAS mail, their other rake which goes to Northern/Western parts of India, it does become a problem especially during months of fog etc and also due to other reasons.