It’s calculated per player unfortunately. It’s not a very ‘smart’ system. So it calculates the most amount of bans per player when playing, so: 9 maps / 6 players = 1.5. It then floors the value to 1 and does that: 1 * 3 players = 3 bans. It should really be floored after the multiplication honestly…
Edit, created a bug report about it: