The Alder Lake-S chips would get 6 more cores over the current Comet Lake-S models, and the difference in size reflects this to some extent. However, the bigger chips also require a new socket, so Comet Lake-S users will be forced to upgrade the motherboard in case they want to make the jump to the 10 nm big/small architecture.
https://www.notebookcheck.net/Leaked-Intel-Alder-Lake-S-picture-shows-the-size-difference-between-LGA1700-and-LGA1200-CPUs.498048.0.html
"Intel also intends to release the Rocket Lake-S models with the same big/small design,,,"
Rocket Lake-S is not a big/small design.
"the LGA1200 socket introduced with this year's Comet Lake CPUs could be abandoned by next year."
The LGA1200 socket will support Rocket Lake-S next year.