Agatha Syphons Power only When Blasted First?
Agatha Harkness assembles her coven (allegedly) to assist in opening the gate to the Witches Road. Earlier Agatha explains that she absorbs power by being blasted first as seen in WandaVision. Agatha then tries to bate the members of the Coven but none fall for her verbal scam. I seem to recall Agatha attacking the entire Vision family and Wanda attempts to protect them by building a shield around them. Agatha then starts siphoning the power from that shield further weakening Wanda.
A little misdirect by Agatha or just some refinement of the Rules of Darkhold Magic wielders?