Ancient post suckered me right in! Oh, well...
Depending on how dry your pellets are, which pellets you're using, your elevation, humidity, etc., you will need to experiment to figure out how deep to fill the tray, figure out how fast it will burn, and therefore, how much you need to fill the tray for any given length of time you want to have smoke.
I never use the MES's built in chip smoking gadget. In fact, I took all of that stuff out of my MES because I only used the Amazin pellet maze tray after I got it and found out how much better and easier it was.
I normally fill the tray completely only when doing very lengthy smokes, like pork butts which can take 12 hours or more. For shorter smokes, I fill less of the maze, as needed.
You can control the rate of smoldering of the pellets by adjusting the airflow through the smoker. I am at a high elevation, so I normally have the top vent fully open and the chip loader completely removed. If I do want to slow the burning, I normally do that by inserting the chip loader and adjusting how much it chokes off the air entering the smoker rather than shutting down the top vent.