BatchCursorFlux respects the batch size of its BatchCursorPublisher if any is specified (see BatchCursorFlux.calculateBatchSize). Currently the method ChangeStreamPublisherImpl.withDocumentClass creates a new BatchCursorPublisher but does not propagate its batch size (if specified) to the created BatchCursorPublisher.

I discovered this while trying to run poc-change-streams.json (POC unified tests) with a reactive driver.