Great---That's pretty much like I said above.
The things you were originally doing were for those who have trouble keeping their AMNPS lit, which is usually the only problem.
It isn't often that the problem is burning too good---That used to be the problem with the AMNS with Dust instead of pellets.
So I would say keep your chip drawer all the way in, and pull your dumper out an inch or so to start, but if it gets to burning real good push the dumper in. Then if it gets too light, pull it out a little again.
Use that dumper to your advantage by using it "Out for more Air" and "In for less Air".
And yes that is the right place to put it in a Gen #1 MES.
And I have found the easiest way to protect the AMNPS from Drips is to take a 9" X 11" Foil pan & cut it in half the long way. Then take one half & turn it upside down & put it above the AMNPS, with the cut end on top of the Empty water pan, and the other end resting on the brackets on the wall: (See Pic below)
Save the other half of the pan for when the first half gets too crummy.
Bear
Which way do you point the can? I imagine either facing down towards the ground or up to the sky. My gut says downwards to create an overall bottom to top of smoker flow (same as with a mailbox mod). Any specific reason for an elbow vs just a straight ducting section with the can at the end?
Your latest test, where the AMNPS went out makes it look like air flow is at the root of the problem. This reminds me of the solution I came up with. (This was prior to building my own version of the "mailbox mod," something which completely and totally fixed the problem of too-fast or too-slow burns). Here's the short version of the story.
I read a lot about people pulling the chip loader out a little, or enlarging the chip loader air holes. The former "solution" seemed to be too inconsistent, as you just found (how do you get the chip loader tube pulled out to the exact same position each time?). The latter solution irrevocably alters the function of the smoker and it may, or may not, ever function the same again. What if you make the holes too larger?
Many months ago I posted in some other threads my simple mod to take avoid both problems I replaced the chip loader with a duct elbow that has a tin can attached to it. In the end of the tin can, I drilled five holes that are larger in diameter than the three holes in the chip loader. This provides several times the amount of air that can make its way through the chip loader holes. I've shown this pic before, but here it is again. The crinkled end goes into the chip loader hole. If I make the holes too large, I simply get another tin can and try again. This can, as shown, worked pretty well.