The problem I have with a receiver that is not chosen by Mr Powell is that it gives him a cast-iron get-out if the test fails. This has nothing to do with his claimed 100% ability and everything to do with the fact that he could accuse the JREF of bribing the receiver to incorrectly receive the results. Mr Powell should be asked to nominate an incorruptable receiver of his own choice.
Also I'd like the test to be much more rigorously timed. For example, if the test starts at 09:00 then I'd like the timings to be stipulated something like this:
Transmission room:
09:00:00
Roll dice, record and sign (volunteer and Powell) result of dice roll.
09:00:15
Start transmitting
09:00:45
Stop transmitting
09:01:00
Roll dice, record and sign result of dice roll.
etc.
Receiver room:
09:00:15
Start receiving
09:00:45
Record result and sign (volunteer and receiver).
09:01:15
Start receiving
etc.
You would also want to video everything that happens in both rooms, and check the synchronisation of the clocks after the test.
The problem with stricter timing is that if someone drops the die, the test is no longer valid.