The indexing that supports postcode searching is based on full post codes. This fits with the use case described in the opening post, where a client provides their postcode as a way to locate issued invoices. We may change this in the future, but it will require a slightly different indexing approach.
I think for those postcode areas that span across England and Wales (e.g. CH), we decided to take a more risk averse approach and just show a Union Jack. It’s very delicate ground and I’m sure if we had more granularity we’d be making a rod for our own back 