Even during a combat heavy day, it can vary vastly. I've run many many EL-5 or so encounters back to back, for instance, and that would slide the scale pretty far that way.
Looking over the past 5 sessions (hooray for records!):
one session ago: 2 (EL-1 and EL+3)
two sessions ago: 1 (EL-6)
three sessions ago: 3 1st day (EL-3, EL-3, and EL-0), 1 2nd day (EL+1)
four sessions ago: 5 (EL-0, EL-0, EL-0, EL-4, EL-6)
five sessions ago: 1 (EL+2)
Each session consists of roughly one week, usually one of those days involving combat.
EDIT: I find it funny that my most combat heavy day has some of the highest EL combats in it.