Shiur hafrasha and nesina - pesachim 32

Tosfos Pesachim32b asks why 1 stalk of wheat is sufficient to fulfill terumah on an entire haystalk when the Torah uses the term "nesina" by terumah which entails a shiur of at least a perutah? Tosfos limits the application of shiur to "nesina" used in the context of tashlumin. One could answer the kashe of Tosfos by distinguishing 2 dinim in the mitzva of terumah: 1) the hafrasha, which removes the issur tevel from the haystack, for which a single stalk of wheat is sufficient; 2) the mitzva of nesina to the kohein, which should be fulfilled with a chashuv shiur. See the Mishne l'Melech in Hil Matnos Aniyim 6:7 who discusses this issue.