The UAT in my Phantom has been laid flat on it side like you have pictured for around 150 flights. One flameout when I ran out of fuel. (Having too much fun!) Make sure and purge it throughly, I typically fill at least the UAT and let it with fuel in it for a while, then fuel the airplane all the way up. Start the engine and shake the airplane. I usually do this at mid throttle settings then run the throttle all the way up and shake the model again, usually on the ground. Make sure and flivk your fuel filters with your finger while at full throttle to dislodge any air bubbles there as well. If you don't pull all the fuel out of it you will likely never need to purge it again.