Cosmo is my 6 month old Biewer and about 6 pounds and he gets 1/4 cup 2x a day. I also give him one NV Medallion for dinner and when we went to the our vets a few weeks ago he was pleased on how Cosmo looked and felt. He said to keep the amounts the same.
I would have loved to have Cosmo on Orijen as I only heard great things about their food but the protein level was too high for him at 40% or more and he was drinking a TON of water. Since switching him to a 24-28% protein level he is drinking way less and pee-peeing way less. OMG he was peeing every 15 to 20 minutes.
I think you are fine..hey trust me they stop eating when they have had enough.