@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

@Lady ​

is “assume that” imperative or subjunctive

@aescling "assume that" is just a long form of "assume"; cf. "assume that it be the case that"