(Holy) BiS Neck Enchantment - Mark of the Ancient Priestess?

[MarcVW]

Hey,

So the decision is probably between "Mark of the Trained Soldier" (+300 Mastery) and "Mark of the Ancient Priestess" (Healing Proc).
I raid semi-casually in a Heroic guild, currently at 6/7 HC.

My math is the following:
300 Mastery = 1.1% Mastery minus Mastery overheal (20-40% depending on encounter) = roughly 0.7-0.9% of Total Heal.
Ancient Priestess = average heal of 0,7% of Total Heal (see log below)

But the later does go up to 1% of total heal in fights, where group is stacked (Ursoc / Xavius).

So, my question: My guild currently progresses on Heroic Xavius, where Ancient Priestess surpasses the 300 Mastery. Therefor I chose the Ancient Priestess Enchantment, but everywhere i look around every healer is playing with the Crit Proc / Mastery Enchantment. Is my math flawed? Can someone tell, whether I'm just stupid or missing the obvious?

Thanks in Advance.

Log: warcraftlogs DOT COM /reports/nLHPzK6wtmNxDgjY#type=healing&boss=-2&source=13

[Nephthysis]

Ancient Priestess is uncontrollable and does not scale with spellpower. People just prefer other avenues.

If it's giving you more healing then by all means, use it for now. It won't hold up as your gear gets better though.