I don't have a gravity feed cooker, so feel free to tell me to get the heck out of here, but...
I guess I don't see the correlation between placement of the guru probe and over cooking. Placement of the probe will mostly likely affect the pit temperature, but unless you are relying on the Guru to tell you when the food is done all that will affect is the cook time. Rely on feel for the big meats to tell when they are done instead and you won't over cook them. For ribs rely on the bend test or toothpick test. As mentioned above you just need to check sooner and more often until you get a feel for the pit. If the temp is consistent from cook to cook that's all that really matters.