While reading their Introduction to the Pentateuch, similar issue arose in my mind also, with a similar conclusion to your Dave. In the intro they state,
'By analyzing the contextual usages, a single English word was first selected as the most suitable equivalent for each Hebrew word. To achieve readability
some words were then given a limited number of idiomatic variants that are harmonious with the sense derived from the investigations.
English words used as the common translation of particular Hebrew words, and even idiomatic variants, are not used for other Hebrew words.'
Does your example fall under 'a limited number of idiomatic variants'?
But I am not sure that I really understand the last sentence: 'English words used as the common translation of particular Hebrew words, and even idiomatic variants, are not used for other Hebrew words.' Does it mean, in your case, that the 'idiomatic variant' used for 'wrath' is not used elsewhere [to cover another Hebrew word]?