I don't know why you say 'at least half', but the parties that got less than proportional number of seats (usually everyone except the CDU and sometimes SPD) ge

I don't know why you say 'at least half', but the parties that got less than proportional number of seats (usually everyone except the CDU and sometimes SPD) gets Ausgleichsmandate ([leveling seats](https://en.wikipedia.org/wiki/Leveling_seat) https://en.wikipedia.org/wiki/Leveling_seat)) so that the parliament as a whole is representative proportionately to the second vote (excluding parties with less than 5% of votes).