Complex sentence: Even though proportionality is confined to the proportional seats to prevent a part from being overrepresented, several restrictions apply in the assignation of the seats; namely, that no party can have more than 63% of all seats, both uninominal and plurinominal.
Split into simpler sentences: Even though proportionality is supposed to prevent a party from being overrepresented, several restrictions apply in the assignation of the seats. No party can have more than 63% of all seats, both uninominal and plurinominal.