I may have noticed the trigger for the Heroic Version.

If you look closely at the Vex Gates on the side towers you'll see slots on either side of it (best seen at 2:54 & 4:43 of the above video). Maybe you're supposed to insert the Arc Charges into those instead of using of putting them in the center. Furthermore, I thought it was odd that the Keeper drops 2 charges, but the plate only needs 1 to deactivate.