Smoking Ribs, temperature question

I have an Akorn

I am doing baby back ribs. As an experiment I have two probes in there and the dome temp. One probe is in the middle on the grate with a pizza pan diffuser underneath. The other is on the edge of the grill grate outside or on the edge of the diffuser underneath. The third is the dome thermometer.

The three readings:

Middle grate probe 231
Edge grate probe 319
Dome probe 252

Which one should I go by. I am going by middle grate probe, to get close to 225, Is the edge one so much hotter cause the heat coming around the diffuser? Where should I position probe for 225? I feel outside ribs will cook faster than the ones directly over the diffuser. Thoughts?