Ok, the tank I just posted is my highest, to date. From what I've been able to experience, a grill block helps.
I tried a grill block by just blocking off the inlets with packaging tape, which looks pretty ugly and it did have some positive effects. I changed to a cardboard shaped grill block, with more of a lower nose to it.
With this change, I have had my highest mileage tank, so far. This tank was a combination of about 2/3 freeway and 1/3 city, although a good portion of the freeway driving was stop and go traffic.
Highly recommend this modification. It appears to be capable of delivering 5%-10%, in my experience.