chakira in how shutfus works as a ptur from certain mitzvos

I want to get back on track with some more lomdus. The ambiguity over whether kesivas sefer torah can be fulfilled b’shutfus (see previous posts) is created in part because the topic is not addressed by the sugya in Chullin 135. The gemara cites a dispute between R’ Ilayei and the Chachamim whether shutafim (partners) are obligated in the mitzvah of reishis hageiz, donating the first shearings of sheep to a kohein, and debates whether the dispute is local to reishis hageiz or applies to other mitzvos as well, i.e. are shutafim obligated in terumah, challah, mezuzah, tzitzis, etc., to give a few examples mentioned in the sugya. Where two partners own a flock of five sheep (the minimum shiur for reishis hageiz), one can understand the debate between R’ Ilayei and the Chachamim in two different ways: 1) the focus of debate is whether each partner is viewed as the owner of all five sheep owned, meeting the shiur to be chayav, or is each partner considered the owner of only two and a half sheep, less than the shiur; 2) each partner is considered to own the minimum quantity of five sheep necessary to be chayav, but the debate is whether ‘coroporate’/shutfus ownership is considered qualitatively different than personal ownership and does not create an obligation in the mitzvah. The first approach sees the issue of shutfus purely in quantitative terms, the debate focussing on how much is owned by each party; the second approach focuses on the qualitative difference between shutfus and other forms of ownership irrespective of the amount owned between the partners. To be continued...