So these properties that you keep in alfresco-global.properties are same as these :
You override the above properties in alfresco-global.properties depending on the type of setup. These properties are useful for generating the user accessible urls. e.g. Url to a node that get accessed either on alfresco host or share host.
You use this utility to generate alfresco or share urls. : https://github.com/Alfresco/alfresco-community-repo/blob/master/repository/src/main/java/org/alfresc...
it intern uses sysAdminParams implementation: https://github.com/Alfresco/alfresco-community-repo/blob/master/repository/src/main/java/org/alfresc...
Please review above classes carefully, you can also try using the utility in a java backed webscript to see how they work. Alfresco itself uses these utilities internally for several cases. so make sure you keep these properties intact and do not remove else it will try to take defaults.
Now when it comes to communication from share to alfresco, it is not dependent on alfresco-global.properties rather, it uses config based in share-config-custom.xml: https://github.com/Alfresco/share/blob/develop/packaging/distribution/src/main/resources/web-extensi...
When you have acs on different host, you update the above config to point to acs host, it could definetly be configured to use either http, https, proxy etc. Its up to you. so to be clear share to alfresco communitucation is not dependent on share.host, share.port or alfresco.host, alfresco.port.
Hope it helps.
(ACSCE, AWS SAA, Azure Admin)