How come I can only choose 'all contacts' and not define a contact subset to sync with?

For some apps we support, we only sync ‘All Contacts’ and therefore, no subsets:

For a couple of apps we support, we don’t offer the availability in the dashboard (yet), to filter and define subsets of your contact to sync with. Here below, you can find an overview of the apps where this is currently the case, the filter is “all contacts” by default.

EXAMPLE ZOHO CRM, there is no drop-down menu to further define the subset of your contacts. 
We are always working on improving our product: our engineering team is working hard to update the connector apps listed above and add filtering so you can also define contact subsets for those.
How does this translate when setting up Multiple Rules?  Find out here
How does this translate when setting up a sync, defining the filters? Find out here