Thermometer questions

I'm hoping to get some help with what thermometer setups/locations work best for you and your WSM. I mounted a 3" Teltru with 2 1/2" stem in the lid opposite the vent. I also have a Maverick ET-73 that I have tried monitoring grate temps with questionable consistency. On my last cook, out of curiousity, I dangled the smoker temp probe thru the top hole of the vent the approximate distance in as the Teltru stem. The temperature readings were significantly different between the two thermometers, by as much as 40* and never closer than 10*. I did the boil test tonight and both were within 2* of each other.
What I'm trying to do is find a location where I can get a consistent reading with the Maverick for overnight cooks and know that it is a true reading. Also, i'm wondering if I should have gone with a Teltru with a 4" stem to get a little deeper into the smoker.
I would appreciate any thoughts or suggestions and to know what you have found that works well. Thanks in advance.

The location of the stem thermo (where you drill the hole) is more important than the stem length. The lid is big and there's so many places to drill and at all kinds of angles, that's the main problem. A 2.5" stem and if you put it at the same height as the lid vent = major differences in temps at the grate. I use a 6" Ashcroft angled down toward the grate and the end of it is just inches above the top grate. Yes it can get in the way at times but there's always a gap to squeeze it in between the meat.