okay guys,
parliament = legislative = Ständerat/Senate and Nationalrat/House of Reps)
government = executive = Ministers/Federal Councilors/Bundesrat
to answer OP's question: There's no need for ALL Federal Councilors to have fixed, PERMANENT seats in the parliament, as they are hardly present and have NO power in this chamber. They just join debates for consultations/ceremonies BUT logically cant vote.
heres a picture of the governements room, where they actually MUST have their individual seats (plus extra seats for secretaries and chancellor=chief of staff)
check out also the Senate/Ständerat
http://www.parlament.ch/e/organe-mit...s/default.aspx
you got also "only" 6 seats for Federal Councilors, which is perfectly logical, as during debates, at least one of them joins also the process in the other chamber, the Natinalrat/House of Represantavives. (and vice versa)
Thats maybe the best answer to OP's question.