The electoral system for the Senate was a strange hybrid which established a form of proportional representation into FPTP-like constituencies. A candidate needed a landslide victory of more than 65% of votes to obtain a direct mandate. All constituencies where this result was not reached entered into an at-large calculation based upon the D'Hondt method to distribute the seats between the parties, and candidates with the best percentages of suffrages inside their party list were elected.
Senators with a direct mandate have bold percentages. Please remember that the electoral system was, in the other cases, a form of proportional representation and not a FPTP race: so candidates winning with a simple plurality could have (and usually had) a candidate (always a Christian democrat) with more votes in their constituency.