Glavoid: Gorge/Disgorge Info?

I have killed Glavoid about 10 times so far with low-man setups (THF, WHM, RDM trio) and i died on all but 3 fights. I just want to know as much about the nature of Glavoid's abilities as i can before I waste any more KI popsets.

The ONLY problems i have been having through these fights are Gorge/Disgorge one-shotting me. I understand that these two abilities are earth-based, and having as much earth resistance as possible (barstonra, earth carol II, etc) will supposedly render these abilities survivable - specifically earth carol II which is said to make these abilities harmless (0 dmg reports).

So here's what happened today. tried duoing with a whm after reading some testimonials. We were well-prepared and the fight went very well until the inevitable disgorge insta-kill. i only accidentally healed it once, maybe for 500 max, it only used gorge once, absorbing 500hp from me and a little more from the whm. the first time it used disgorge, it did about 1,400 dmg to both the whm and i. the way i understand it, disgorge is like 1000 needles in that you need more bodies to split the dmg with, so we were both standing in front of glavoid. for the record, again, i am thf, have all stat/hp abyssites, used earth wyrm (earth+100), ebon hoof (superior HP) and RR atmas, along with barstonra and shell V. I had over 3300 HP. the second disgorge is used did 4300 dmg to me and 4500 to the whm.

i understand the best advice on these abilities is to keep them stunned, i just want to understand how the dmg is determined. a friend is telling me the dmg seems to be in multiples of 3000, perhaps doing 3000 split the first time, then 6000 split, then 9000, up to 12000. it's possible the whm stunned the 2nd disgorge and i didn't notice, then its third was split between us for 4500~ each, but i can't square this with my experience from the previous fights where i was healing it for a ton and ate 2 or 3 disgorges (not split, all me) before the one that killed me.

i'm just discouraged now because i stacked HP and earth resistance but none of disgorge's dmg seemed to be mitigated.. so how is it that people are saying earth carol is a necessity if it's just earth resistance, the same as barstonra and the earth atma? i've had good fights where i'm never in any danger and bad fights that kill me from the start. at this point it looks like it's just luck. Am i missing anything or is stun that critical?

thanks in advance for any helpful insight