On Site Servers, Rate Limits are set under \Administration\Overview\Hierachy Configuration\Addresses.
Right click the site name and select properties then the tab "Rate Limits".
For Site systems that only act as Distribution point, Rate Limits are set under \Administration\Overview\Site Configuration\Servers and Site System Roles.
If you mark a server "Site System Roles" is shown at the botttom. Right click "Distribution point" and select properties then the tab "Rate Limits".