Chad, I tried the Quattro full-face mask for a while. I tried all sizes. I found that I had to tighten the bottom straps down very tight in order to prevent leaks with that mask.
I have highly positional sleep apnea. With the Quattro, in particular, I found that I had a much higher AHI, with the apneas appearing in large clusters, when I would sleep on my back. When I restricted myself to side-only sleeping with the Quattro, results were more similar to the excellent results I get with nasal pillows and nasal masks. You may be interested in the thread regarding my "Quattro Experiment":
viewtopic.php?f=1&t=48909. It includes some graphics that show what was happening. I suggest you read both pages of the thread to see the differences in results.
My theory is that the tighter bottom mask straps with the Quattro were pulling my chin down toward my neck, blocking my airway, especially when I was on my back. You may want to experiment by trying side-only sleeping and see if that makes any difference for you with the full-face mask. You may want to consider trying other mask types. I do
very well with nasal pillows + PAPCap chin strap. I usually have either zero or one apnea per night (reported as AI of 0 or 0.1), with zero leak rate. But not everyone will have the same results.
I hope you'll let us know what you discover!