[Exim] search_type syntax help for system_aliases director

I have the following issue I am debugging: I cannot get the
${local_part} to get looked up in the aliasfile. exim wants to use the
full email address to look up the alias. I'm trying to find a good doc
on search_type syntax to only search for local part.

Here is a copy of my system_aliases director:

system_aliases:
driver = aliasfile
file = /etc/aliases
include_domain = yes
search_type = partial-lsearch
user = mailnull
group = mail
file_transport = address_file
pipe_transport = address_pipe



using as a test:
rm -rf /var/tmp/exim.out; ( echo HELO localhost; echo MAIL FROM:
aqw@???; echo RCPT TO: carlos@???; echo DATA ;echo To:
carlos@???; echo ""; echo "."; echo "QUIT" ) | exim -v -bs -d9
2>&1 | tee /var/tmp/exim.out

with output like:
[..]
directing carlos@???
calling system_aliases director
df_lookup entered: search type = lsearch
system_aliases director: partial2-lsearch key=carlos@???
file="/etc/aliases"
search_open: lsearch "/etc/aliases"
search_find: file="/etc/aliases"
key="carlos@???" partial=2
LRU list:
7/etc/aliases
End
internal_search_find: file="/etc/aliases"
type=lsearch key="carlos@???"
file lookup required for carlos@???
in /etc/aliases
lookup failed
trying partial match *.carlos@???
internal_search_find: file="/etc/aliases"
type=lsearch key="*.carlos@???"
file lookup required for *.carlos@???
in /etc/aliases
lookup failed
system_aliases director declined for carlos:
calling userforward director
[..]

$ exim -bV
Exim version 3.36 #1 built 10-Jul-2002 12:57:05

Thanks,
Andrew