When you get a good KM run, which usually happens quite a few times per fight, I use Obliterate when ever I can't FS and have runes for it or can use PL / BT to get runes. This usually gives you a good uptime also on the tier buff.
On Kormrok, I place the defile slightly earlier before the hands on the spot where we stack and have 10+ stacks on BT and runes ready, I also use Pillars before they spawn and a trinket, if using vial.