Open the vault item for editing, then click the gear icon () next to the URL, and select the option Host in the dropdown list of URI match detection options.
If you want this level of specificity for all of your Bitwarden login items, go to Settings > Auto-fill, and set the Default URI Match Detection option to Host (in which case you can leave the match detection setting for the stored URL as Default).
Being that your saved logins share the same base domain, Bitwarden assumes they will be the same across all sites controls under that domain.
You can either change the global default, or change this match detection for individual login items as well.
Typically the Host or Starts with work well, hope this helps