I realize that the OP and others on this thread know the ropes, but in the expectation that some folks are new to these issues, I would submit that one other short term tactic that has worked for me to get further connections is to set the number of results away from default to 50. Never get 50, but usually you get some interesting additional possibilities. Although like all computer searches, you have to keep your sense of humor--as in the search I ran with some specific timings for SEA-SFO that offered a connection on the following SEA-IAD-SFO' then there's always the popular SEA-PDX-DEN-LAX-SFO that came up one time.

Flyer 420
across the street from USC
Los Angeles