The concern felt by the Lumley Family's coach was understandable.
Field Array was a new concept that had recently become a hot topic in the Array community. The idea was proposed with the purpose of imitating a Magus's Domain.
But because a Magus's Domain relied on the mage's magic energy capacity, it was almost impossible to replicate it. Besides, a domain's effect differ from each Magus, making it even more impossible for a Field Array to have fix materials.
Because of this reason, that the required materials and array calculation to create a Field Array was still under debate. And only a few selected factions with their own Array Specialist were able to conduct their research.
To date, only the Royal Army's Research Division succeeded in its creation. Unfortunately, they could only create a six-meter radius array and its duration only lasted for about a minute.