Benham and Ratcliffe Tests

I need to complete an IHT400 for an estate. The Will includes exempt and non exempt beneficiaries, but does not clarify how inheritance tax should be dealt with, nor does the Will file. After completing the calculations for both tests, it appears there is no inheritance tax. I am now wondering whether the Executors still need to agree which test is being adopted and this needs to be shown in the IHT400?