maybe im missing it... but why not use the old and simple proven setup
i use a [target=focusttarget] system in all of my other spells. but had to revert to basic for this


/assist focus
/castsequence reset=target/17 Flame Shock, Lava Burst, Lava Burst, Lava Burst, Lava Burst, Lava Burst, Lava Burst,

the reset target works, due to the assist part, the reset 17 works (with glyph flameshock lasts 18 seconds for me) and will reapply flameshock if a boss encounter lasts more than 20 seconds

downside to this is... in pvp, the people will see who the main target is gonna be due to the assist part....
but dont you think that if a warrior see's 4 flameshocks on him, he's gonna know that anyway