shiur of challah vs reishis hageiz - R' Chaim Brisker (II)

We asked yesterday, why is it that shutafim who jointly own a total shiur of 43 1/5 beitzim of dough (same as an individual) are chayavim in hafrashas challah, but shutafim who jointly own 5 sheep are not chayav in reishis hageiz? Why according to the Rambam does the chiyuv of resihis hageiz require 5 sheep per owner and not 5 sheep b’shutfus in total?
Bill Selliger nailed this one in the comments, so this is just a recap. R' Chaim uses a classic Brisker gavra/cheftza split on this one. The shiur of 43 1/5 beitzim measures a cheftza shel issur; as long as the proper volume of dough is present, even if owned in partnership, the issur of tevel applies until hafrashas challah occurs. However, with respect to reishis hageiz, the mitzvah obligates giving a portion of wool to the kohein but does not create any issur on the shearing. The shiur of 5 sheep is not a measure of a cheftza shel issur, but a measure of who is a bar chaiyuva in giving wool. Since owning 5 sheep b’shutfus is not the same as exclusive possession of 5 sheep, the Rambam paskens that unless each partner individually possess 5 sheep he is not a bar chiyuva.