First of all, welcome to the forum Keith, we are very happy to have you here. Secondly, what a great question! Hmmmmm…
OK, so when you change what POSITION you are playing in, you are changing what KEY you are playing. It sounds like you are comfy with that concept, right? OK, Cool.
Next question: What the heck is a key? Oh boy, that’s not a simple concept to tackle, but to simplify it - it’s the place of greatest resolution and rest. It might not be the first or last note of the song, but if we were to listen to a song, turn it off, and hum what feels like the fundamental “home base” of the song, and then go to a piano and play the note that we are humming, the note name of that piano key would be the name of the key of the song.
Understanding keys is much more complicated than that, but that kinda gets to the heart of the matter.
In the example that you provided, “Smooth Operator” if you were to try this humming excercise, I think we’d probably agree the “home base” of the song is the note Sade is singing on the syllables “-er-at-or.” Right? You with me?
If we did it on “Mary Had a Little Lamb” I think we’d agree the “home base” is the note we sing on the word “snow.”
So if know the HARMONICA TAB of the ROOT NOTE of each position, then we can extrapolate from the tabs what position we are based on this humming excercise. Here’s the cheat sheet on root notes of each position:
1st Position = 1, 4, 7, 10
2nd Position = -2, 3, 6, 9
3rd Position = -1, -4, -8
4th Position = -3", -6, -10
So if you’re playing Smooth Operator -5 5 -4 -4 -4, then you’re playing it in 3rd position (because we determined that note is the key of the song by humming the note where we feel the most rest and the least tension, and we see on our chart that -4 is a root of 3rd position.)
If you’re playing Smooth Operator 7 -7 -6 -6 -6, then you’re playing it 4th position.
It’s also possible (but more challenging) to play Smooth Operator in 2nd position: -3’ -3" -2 -2 -2. (@martorgan if you know this song, this would be another good one to practice your -3’ Bends! 
)
So I hope as you go on this journey that you will come back to this post share your journey of figuring out what position you’re playing in from tabs you’re working on. Great question Keith! Rock on. 