My watcher is a pure class cipher that uses Frostseeker. My party order has them in the 4th slot and they also stand in the back line on the map. I do not use stealth to start fights as the ranged characters attack before melee characters which means they get all the attention. This might be your problem.
Even in scripted events like the dragon with the xaurips the aggro is spread pretty evenly around my party. Then again my watcher always charms as my first action so I tend to turn the tide of battle quickly so I may not be a good example.
Are you starting the scripted events and just letting your party do whatever they want, or are you pausing the game and giving out specific commands to each member?