are phrases like “assume it be that” attested as usages of the subjunctive

@aescling sounds subjunctivey to me

@Lady what i meant was whether this usage is attested

@aescling if the usage is grammatical and you made it then it is attested by you :P

@aescling my guess is that “assume the arrangement be [such] that” is more common than a plain “it” but

@aescling or “assume it be the case that” etc

plain “it be that” operates pretty much entirely to create the subjunctive mood with no trimmings and i think most english speakers today would just drop it if it didn't have anything else to add