[Asterisk-Users] question about type=user in sip.conf

[Michael Ulitskiy]

Hi, 
I may be missing something here, but I don't really understand
how asterisk supposed to handle type=user.
Suppose I have the following config (mostly taken from default sip.conf.sample):

sip.conf:
context=sip   ;default context for incoming calls 
...
register => user at sip-proxy-out
..
[sip-proxy-out]
type=peer
username=user
secret=secret
..
[sip-proxy]
type=user
context=from-proxy

The question is how asterisk determines that the call is from sip-proxy?
Whatever I do all incoming calls coming from sip-proxy (or from any other sip device
not registered locally) get into "sip" context (default context) instead of "sip-proxy" context.
Could anybody enlighten me on this or point out to some documentation?
Thanks,

Michael