I figured out what I was doing wrong
 

After untold rentals with (I thought) few upgrades, the light came on. I have only counted premium, luxury and SUVs as upgrades.

I use ITN.net/my_company_name_here to make all my travel arrangements. Avis is the only car rental option unless I want to be scolded for bending/breaking the rules. Unfortunately, the car group choices I am presented do not exactly match the Avis car groups. I have always selected "standard". The first time, I thought maybe I was going to get a manual transmission :D - turns out this translates to group D - full size 2 door. I always wondered why it was usually the same price as "full size". So, all along Avis locations have been upgrading me to class E - full size 4 door (a technical upgrade but in reality a disappointment).

Somewhere recently ezmonee posted a list of car classes which made me go back and compare reservations to receipts. Lo and behold, most of my rentals have been upgrades.

I just booked my trips for next month and picked "full size" cars. I fully expect to be upgraded to class G vehicles. Hurray for ezmonee! Hurray for Avis!

Now let's see if they can get the price right. :confused:

there ya go. You should start seeing premium more often now.

Thanks for the tip!