It's easy to check OP's speculations, just put Edo Roshi in position 2, fire main with bani chakra position 1. In the beginning of the round, if you have 80 or more chakra and didn't use bani chakra that round, you should queue Edo Roshi's and Fire Main's mysteries at the same time. That way Edo Roshi will have 60+ chakra at the very moment he's using mystery.

Though said all that, I believe what Garv wrote is correct.