New and improved testing now with stairs!
Warning: many shalebacks and jaguars were harmed in the running of these tests
Conclusion: having a possible path to the ground definitely reduced teleporting, only one instance in the whole batch. With stairs down they pretty much stayed put even when their behaviour (prefer ranged instead of stand and defend) would permit them to come down stairs to maintain line of sight (los) which I considered a fail. When the stairs were removed and the wedge pillars raised to the height of the walls the archers would take a step back onto the wall when the test subject got too close which would break los and once again they would not use the path available to them to regain los. On only one occasion did they actually use the path to get back into los.
I would say that I think the archers are trying to maintain a minimum distance from their enemy. Without a path they were teleporting, when the stairs were there but there was an angry Jaguar on them archer 1 teleported over to archer 2 and then the ground. With the wedges being brought to the height of the wall they were taking the step back, possibly that was enough with the height of the wall to maintain distance but I didn’t run a huge number of tests.
Thing is when I first noticed the teleporting I had an entire 30 foundation long wall of archers all teleporting all over the place, the ground, on the wall and onto awnings so either they have a very extreme definition of personal space or this is just coincidence and not causation.
UPDATE: logged in to check the length of the wall and the Jaguar who lives outside my base was waiting for me, I suspect he is a bit fed up of being killed during my testing! He jumped me as soon as I went out of the gate so right next to the wall and the 2 archers who I had left on their pillars this time did not step back onto the wall, they had a bit of a think before they started attacking but they did attack and remained on their pillars. This was a fresh log in so it could still be a case of the issue getting worse over time?
Tests
2 archers once again with the settings
— Attack everything
— Attack distance 50
— Chase distance 50
— Prefer ranged attacks
(thrall doesn’t have melee weapon in his/her inventory)
Test 1: Stairs were built down from the wedge pillars providing them with a clear path down to the ground
a. shaleback in mid range: both attacked, shaleback went up the stairs to go for archer 2, archer 2 kept backing up but did not leave the pillar 
b. shaleback close to wall: both attacked though archer 1 took a while to work up to it, both remained on pillars
c. shaleback at the edge of their range: both attacked and remained on pillars
d. jaguar manually spawned (lasts longer than a shaleback) at edge of range, pulled in and out of range: archers attacked, stopped when out of range and resumed when back in range, both remained on pillars
e. jaguar close to wall between pillars, pulled under stairs to break los, eventually pulled around corner completely out of los: both archers attacked and stopped when los broken, did not come down stairs to get los back, remained on pillars 
f. jaguar outside base respawned: archers attacked, jaguar went up stairs to archer 1, archer 1 teleported over to archer 2’s pillar and then teleported to the ground (did not use stairs)
g. jaguar in los for archer 2, not in los for archer 1: archer 2 attacked and remained on pillar, archer 1 came down stairs to get los, once fight over returned to a spot on the ground to guard instead of returning to original position (fail because while coming down the stairs to regain los is fine as he is prefer ranged and not stand and defend, he picked a new position on the ground for his guard spot instead of going back up the stairs to his original position)
h. jaguar in range pulled in and out of los: archers attacked when in los but stopped when los was broken, did not come down stairs and remained on pillar.
Test 2: Stairs removed and another wedge placed on the pillar raising them to the height of the wall which has stairs to the ground giving the archers a clear path to the ground
a. shaleback in mid range: archers moved back onto the wall, had a ponder and then moved forward onto the pillars and started attacking, remained on pillars once attacking. 
(Pass because they did attack but also a fail because only after having to discuss it amongst themselves)
b. shaleback close to the wall between the pillars: archers backed up onto the wall and never attacked
c. shaleback at edge of range: both attacked and remained on pillars
d. jaguar respawned, started at range and was kited closed to the wall: archers initially attacked but when jaguar got too close to the wall backed up onto the wall and stopped attacking
e. shaleback at edge of range, pulled in and out of range: archers attacked when in range and stopped when pulled too far, remained on pillars
Test 3: Behaviour changed to Stand and Defend
a. shaleback in mid range: archers attacked and remained on pillars
b. shaleback close to wall between pillars: both archers moved back onto the wall and did not attack
c. shaleback in mid range for archer 1 and close range for archer 2: archer 2 moved back onto wall and did not attack, archer 2 attacked, when moved out of los for archer 1 stopped attacking but did not move from pillar, resumed attack when back in los
d. shaleback at edge of range, pulled in and out of range: both archers attacked when in range and stopped when out of range, remained on pillars