What is the burden of proving severance from a joint trial?

[t]he party seeking reversal of a decision denying severance under Rule 14 has the burden of proving "clear," "manifest," or "undue" prejudice from the joint trial. Such a party must show more than that a separate trial would have given him a better chance for acquittal. He must also show violation of one of his substantive rights by reason of the joint trial.... In other words, the prejudice must have been of such magnitude that the defendant was denied a fair trial. Clearly, this is not an easy burden to meet.

Id.; see United States v. Sherlock, 865 F.2d 1069, 1078 (9th Cir.1989).