Ducal Guard, Zenith, Earth Wyrm on VE

[Niyariko]

Does Ducal Guard activate @ 50% automaton's HP?

I was doing some test today on VE, with DG/Zenith/Earth Wyrm. I didn't notice any big difference in Damage Taken until my VE reaches below 30% HP.

But on DG alone, I should have received 50% -dt @ 50% auto's HP.
Was testing on Tought Sand Sweeper at abys-altepa and with Equalizer, Armor Plate II, Barrier Module, and putting at least 2 earth maneuver most of the time .

Does anyone know why DG kicks in @ 30% HP instead of 50%HP?
or was I seeing things!?