twitter and facebook as graph hosts

whats your model for using twitter, facebooks, and proxy URIs etc? Ive understood that when getting a cert from your site, it builds a profile (distinct from the original foaf card that I continue to maintain). Lets call it a master-card :-). And, I understand that said master card can be hosted on an ODS endpoint, known as a proxy. Even though my webid is within http://twitter.com, I get another webid called http://ods/x/y/z/http/titter/com.... or similar, where the latter is a particular structured name. Called a proxy URI, it points to the master-card, which wraps the original card. A sparql call on the proxy can make queries againt properties in the master cards and its subcards. now, where is the master-card stored?  Is it stored in twitter read/write store (since I granted a OAUTH write session to my twitter data space)? Is the twitter page referenced by my tiwtter webid supposed to show the RSA key? for the facebook case, is it stored in a facebook graph store? Is that graph, when search my machines using the facebook API, supposed to bne able to see the RSA key? In all cases, when I use my webid/cert at FCNS, and Ive stored both the twitter URI AND the proxy URI in the cert's SAN fields, it will try both stores. Is this the way to think? Is this how I SHOULD use multipl SANs (to point to different places here the key might be found, in some kind of inheritance/containtment relationship)?