There does not appear to be any string which can be used in securetty which will allow network root logins as documented. In previous versions, ttyp1, ... worked. In 6.1 (and 6.0 I think) a logged-in user shows, e.g., pts/1, but using that string in securetty still does not permit a root login. Removing securetty entirely does allow root login as documented. This indicates that the problem is in fact in the interpretation of the file.
I've tried to fix this in pam-0.72-4 - a workaround in the meantime is to put just the plain tty number (without the 'pts/' prefix) into /etc/securetty. Putting anything other than local ttys in securetty is meaningless though, because there is no guarantee that a particular individual or source host will be assigned to a pty. The possibility is very real for anyone to deny you root access, or alternatively gain root access themself. You'd at least avoid the DoS attack by turning off securetty altogether.