Ways to have a higher T13 parse:

Limited/no Earthshakers (or at least being Covered)
Having another melee do LB2/LB3 in final phase (whichever your group gets)
Doing no orbs, running out for orbs = DPS loss
No stopping DPS of any kind for an easier transition
Not breaking off to fight the wyverns that spawn or moving boss
Having crappy DoM (ALL DoM, not just BLM/SMN) in add phase who can indeed steal everyone's numbers, or just crappy other players who will let you have longer uptime in an otherwise fixed amount of time
Minimal/no Megaflares, depending on stack location/point in your rotation it can be pretty bad to get Megaflares
More uptime on boss in final phase. The more time you're fighting the boss here, the less % of the fight the downtime of the add phase is
Typically not a big deal but occasionally doing a pylon/tower/exploding thingy can hurt positionals so the less you do the better, technically

I actually really dislike T13 number comparisons between groups and even repeated personal numbers, it's one of the most RNG and strategy impacted turns in the game even if at first glance it's just pew pew mostly.