You should be able to increase 'max_search_size' config entry to 1000 on the server.
If it's not possible your Find on premise might be very old.
This was resolved by setting the max_search_size to 1000. This was choosen when the index was created, but did obviously not get registered.
This is possible to do directly on the index (thanks BV Network).
Further runtime settings are stored in a special `@admin` index, mainly for use
by the `es-proxy` service. The settings are normally viewed and adjusted through
the web index admin interface, but can also be accessed directly:
$ curl -XGET "http://localhost:9200/@admin/_search?pretty"
And even updating the relevant `key/_id` document directly:
$ curl -XPOST \
> "http://localhost:9200/@admin/key/XXXXXXXXXXX/_update" \
> -d '{"doc":{"max_search_size":1000}}'