Askenazi in non-Ashkenaz minyan

Q: Should an Ashkenazi Jew davening with a Sefardic or Nusach Sefard minyan say Tachanun when they are saying the Vidui or when they also put their heads down?
A: It does not matter. When he is the only one in the minyan who is Ashkenazi he should also say the Vidui because of "Lo Titgodedu – do not make different groups," but today most minyanim in Israel are mixed. By the way, it is explicitly written that when the community is saying Aleinu one should also at least bow when others do, since it is said at different times in the davening.