My answers are in RED
I am going to use my AMNS for the first time this weekend in my Masterbuilt XL to do 2 butts and have a couple of questions. Since I have plenty room should I put the AMNS on the bottom next to the burner or above the burner in a pan? Try it both ways to see which works better. Either way, you'll need a heat deflector between the flame and the AMNS.
Should I fill the AMNS or leave the center row empty (6x8)? If I fill completely do I light just one end or both ends? I would light both ends and leave the center row empty, to keep it from jumping rows. You should get about 4 hours of good smoke this way and can refill if nesessary.
If I use on the bottom next to the burner I might drill a hole beside the AMNS for some combustion air and put a piece of ceramic tile between the burner and AMNS. I think this may be a good location and the tile will work as a great heat shield. Yes, you need some intake air for good combustion.
I realize the AMNS works best at lower temperatures but it seems some of you guys are having success at higher temps. You're correct, but there are a couple tricks guys use to get it to burn at higher temps, without jumping rows. You really need to keep it out of the direct heat from the flame.
Here's a pic from Richoso, where he placed his AMNS in a GOSM. I know your Masterbuilt is different, but the placement may work the same. It is directly in front of an intake vent.