The Parked Domains feature allows you to point a domain to your main site /public_html folder.
You can still use the redirect option under cPanel -> Parked domains and redirect a parked domain name to a sub-folder for your main domain. However, this will not keep the parked domain name in the URL. You will be redirected to a subfolder for the main domain.
In order to have a domain name pointed to a specific subfolder, you need to configure the domain as Addon Domain.