Turn meter caps out at 100%, there's no fractions or numbers above that. So if multiple characters are ever tied at 100% the game will randomly determine which of them goes first. It's constantly doing this and updating after every action--you can tell if you ever play Resistance and have your entire team at 100%, very often a character will get two or even three turns before one of your others gets even one.
The way the game gives Han the first shot is to fill his TM as soon as the battle starts. Since both Hans have 100% TM, the game will randomize who goes first. If it's Galactic War and you're playing Resistance, you will occasionally see your characters going before Han if all of them also have 100%.
Or if you're playing Droids and have BB-8 and HK on the same team, come to think of it. Basically anyone who gives big chunks of TM at the start or end of a battle.