So, what is a tower in your perspective 
So that I can make such one and test it there.
So, what is a tower in your perspective 
So that I can make such one and test it there.
A SUMMARY:
I have made some tests with archers recently and found a way to place archers on an elevated building piece (without stairs to the ground) so that they DO NOT TELEPORT TO THE GROUND, even if the line of sight with the target is interrupted or the target moves out of range or even out of render distance.
With the following test setup that works:
(*) As @Wak4863 pointed out, you can chose “prioritize ranged” first, and then “stand and defend” from the tactics wheel to make sure the thrall does not want to melee. Although it sounds strange to me, maybe it helps.
I jsut put up a big post, summing up current thrall issues. @r4nd0mGamer I have tons of different setups for archers, including yours. Sooner or later they still teleport.
I’m not overly concerned about kill pits. As I’ve said before they’re merely a convenience/luxury.
My strong concern remains the fact that archers and pets I’ve placed atop bases are still teleporting down to (or even thru) the ground mesh, and purge attackers are ending up atop bases or teleporting thru walls.
Regardless I’ll give your settings a try later on and see how they work, though that sounds awfully similar to revisions I’d already made after your previous experiments.
Starting up the game… Will try with stand & defend -> then ranged.
Then will replace triangle with normal ceiling piece.
First update: Came to my outpost and the archer was ported down, without any door behind her…
Second update: So setting her to “stand and defend” results in no porting down.
But then again, removing the door also looked like it is fixed, but after 1 week she was down…