To the many you shall increase his inheritance, and to the few you shall decrease his inheritance; each according to those counted of him shall his inheritance be given.
Torah Temimah: Sifrei
English: It was taught: if at the Exodus he had five sons and at entry into the land ten, I apply to them “to the few decrease his inheritance”; if ten left Egypt with him and at entry five remained, I apply “to the many increase his inheritance.”
Double counting rule for ancestral vs entrant generation.
Share size tracks both the Exodus generation and those who entered the land.