I always thought, that at least the editor and many authors were aware of the potentially devastating use of movable Aegides in assaults - and when it came up in LoH acted decisively, without spelling out the problem.
Anyway, here's a short summary of it.
A movable Boundary can be anything, from a ring of rope to more stiff light metal rings - may be even kept rigid by magic. It all depends on the house rule on boundariness to be kept if the Aegis cast with this boundary moves. Such an Aegis of assault can by magic be moved fast and silent, even teleported in an instant, turned invisible and protected against many kinds of detection, mundane and magical. The magi protected by it can then slap it - in a single round, if needed - around any reasonable area with inhabitants, traps or magical threats they wish to eliminate or subdue, benefiting from its all-around protection.
So this changes many published adventures, and many sagas, significantly.
An adequate variant ArM5 p.161 Unravelling the Fabric of (Vis) can be easily put into a high penetration lesser enchantment (the Wand of assault) able to easily bring down an Aegis in a round as well.
Wand of assault and Aegis of assault together can replace the Aegis of any covenant in two rounds by one protecting the attackers, not the defenders. So they reduce every covenant remotely threatened by devious sodales into US aircraft carriers in the south china sea: on constant high alert!
They have to anticipate an extremely fast attack they can only prevent, if everybody is always on the magical lookout, detects the invisible Aegis of assault in time to bring its own Wands of assault to bear before it lands. No study, no experimentation, no recuperation: just alert!
Doesn't look like Ars Magica to me. 