So did a bit of playing around very late at night (aus prime time) with noone else in zone, to attempt to explore these mechanics some.
A few things to note we tried this with people who are:
non-kos ROS & COV.
kos ROS & COV
kos ROS & non-kos COV.
Results did not vary.
First video shows me parking an ice burrower directly on top of sontalak. Casting harmony with IB targeted shows a resist (from sontalak, belly caster) however the burrower is harmonied (a non kos was able to run past).
I then direct target sontalak and cast harmony, and it aggros.
https://youtu.be/wQr7rQyoOLM
Second video shows doing similar with bind sight from outside of leash range. Casting direct on sont = FTE message and resist, however cycling target TO sontalak after cast starts results in normal expected bind sight use, with no aggro etc.
https://youtu.be/4BHpTTNWvu0
We tried with esorpa, and a wyvern, and a burrower (@sont ensnared and unaggro) to attempt various factions.
Hope this may help somehow. But to any people in the raid scene, at least if you MUST bind sight 100% MR and/or belly cast raid mobs, do so by cycling target to the mob after the cast starts.