Trust NPCs Are Inconsistent in Griaule Fight

Date & Time: 4/15/20 6:20AM PDT
Frequency: Always
World name: Gilgamesh
Character name: Unquenchable Fire
Retainer name: n/a
NPC name: Ryne, Urianger, and Thancred
Monster name: Griaule
Class/Level: SAM 74
Party or solo: Trust
In-game time: 11PM
Area and coordinates: Dohn Mheg 11.3, 9.0
Housing: n/a
Steps:
1. Start Griaule fight
2. When the unnamed sprout adds spawn, stand in one of the tethers on the opposite side of the boss from the Trust NPCs.
3. Watch one of the Trust NPCs come all the way across from the other side of the boss to stand in front of you, leaving two of the tethers open and giving Griaule two Growing stacks.
4. Try taking one of the tethers on the other side of the boss at the next sprout spawn so the NPCs will take a tether.
5. Watch one of the Trust NPCs come all the way across again and take the tether you are standing in.
6. One more round of same and the boss is at full growth
7. Die when the boss casts Tiiiimbeeer the next time.

Summary: I'm expecting the Trust NPCs to take the tether closest to them and they're picking one at random, as far as I can tell. I've literally seen both Ryne and Urianger start standing in a tether and walk away from it to take one on the opposite side of the boss. This makes it difficult to guess which tether I should take and hard to avoid TPW when the boss gets all the Growing stacks.

Also, if this report is incomplete, please let me know what further information it needs to be complete or clear. I can include the hardware information that I cut off, but I'm not getting lag or having performance problems with the game in this instance.