Geocoding Structured Query when using alternative Providers

We are currently in the process of adopting Graphhopper for a couple of tasks, one of them beeing lookup of postal codes to filter objects based on their location.

I am currently evaluating the usage of Graphhoppers Geocode API, am however struggling with the generic nature of the APIs query parameter. When I query a postal code, sometimes it will show a correct hit, most times though it will consider e.g. a Street in the U.S. as a more accurate result.

Now according to the documentation the API supports different providers, one of them being nominatim, which according to their documentation supports structured queries. Is it possible to pass those through from the Graphhopper to the nominatim-API?

As we use opencage data not only for their own geocoding provider but also for provider=nominatim it is currently not possible to support structured requests:

Nominatim supports some types of structured queries. We do not.
This is intentional, our goal is to keep the service as simple as possible for developers to comprehend and get productive with our service. Please follow the steps laid out in our guide to query formatting.