Under an option E contract, the Prices is effectively a forecasting estimate of no contractual significance in terms of what the Contractor or Consultant gets paid.
Consequently, a quotation with a forecast change to the Prices is just that : a forecast. If however, it turns out to be wrong then it makes sense to revise the forecast out turn of the whole contract.
So, I am not sure if I would describe it as ‘obscure’, but you do need to stand back from the specific contract provisions to make sense of it !