[MW:6831] tempering temperature of P4 material

Dear all

There is a clause in Saudi Aramco documents stating as below

The maximum PWHT soaking temperature for quenched and tempered carbon steel and C-1/2Mo shall not exceed the temperature at which the test pieces were heat treated as shown on mill test reports or 650 deg C max for carbon steel ,690 deg C max for C-1/2 Mo and 700 for low Chrome alloy.

Our material is SA-387-Gr 12 cl2 (C -1/2Mo) which is P4 material. The min PWHT temp as per code (VIII Div 1-U stamp) is 650 deg C.

Now aramco has commented on our documents that they need a PWHT temperature to be 25 deg C less than tempering temperature as specified on MTC for the plates. So we need to have a tempering temp of min 680 deg C  so we can carry out the PWHT at 650 deg C but he plates MTC shows the tempering temp as 660 so we are 15-20 deg below. The plates are already purchased which are 65,70,80 mm thick.

My first query is no where in the aramco document we can find a clause of have PWHT temp 25 deg C less than tempering then what is the reason for asking this requirement.
What is the solution that we can offer them.

Regards
Thaksen