Or HaChaim on Numbers 34:15/אור החיים על במדבר ל״ד:ט״ו

1 שני המטות וחצי המטה לקחו נחלתם, The two and a half tribes took their inheritance, etc. The Torah wrote this verse to indicate that the inheritance of the half tribe of Menashe was part of the overall territory allocated by Moses to Reuven and Gad. Moses did not make separate boundaries for each of these tribes.