How does the game decide who goes first when two toons are BOTH granted 100% turn meter?

My 88 and 86 are the exact same speed. I always want 88 to go first... AoE debuffs everyone, 2nd attack (from HKS lead), then 86 slams them with the double attack.

This is my formula for killing Rey in arena after she gets her foresight on. AoE drops foresight, then wham wham wham.

But at least 50% of the time 86 goes first messing it all up. Needless to say, time for a mod adjustment