It is difficult to find the right spot for the AMNPS in a propane smoker, because as you've discovered the combustion of propane also uses a great deal of oxygen. I don't have the XL so I'm not aware of it's vent system, but I do see in the picture above, a vent, that appears to be on the side. My GOSM has two side vents. The first thing I did was remove the deflector plate of the preferred vent, then created a shelf of sorts to rest the AMNPS on, as far back from the burner as possible. I had to wrap the shelf in foil to act as a heat deflector because without it, the pellets would ignite prematurely.
Here's some vues that may help you:
My GOSM isn't very pristine, but she cooks just great and I don't want to jinx her.
A very early picture in the tests to show: yes you can get smoke.
Yes, you can get smoke. Truth in viewing, this was taken during a cold smoke. I did notice and Todd confirmed in his tests, that "smoke" visibility is different between hot and cold smoking. Cold smoking, you'll see the above. Hot smoke: you'll see what's in the middle picture. Apparently, in the hot environment, smoke becomes more transparent. I don't know why other than to say the heat has something to do with it. You're still getting the precious smoke we all desire. You have to remember, the AMNPS and earlier versions (dust) were intended for cold smoking, but many of us are adapting it to hot smoking. It can be done, but each individual smoker seems to present its own particular problems. BTW, before someone asks, the glass in the GOSM door is a modification I and some others made so we could keep an eye on the Q'ing process, without opening the door all the time. If you decide to mod your door this way, be sure to get oven rated glass. It'll handle the temps you'll see with a propane smoker.
Any further questions? Just ask.