TL;DR - Contribute your address data to Open Street Map and the location will be spot on.
Post code areas are basically based on delivery routes of a 1960’s red Commer van - yes, the system has been improved since then however it was not designed to be used for location. Some post codes may contain one property; another a whole estate of 200 homes. My own home geocodes about 150m away without the property number. Both Royal Mail and OS have other data sets, but…
The next issue is data ownership. The Postcode Address File is owned by Royal Mail who license access to generate revenue. HASS uses Open Street Map for map tiles which is created by volunteer surveyors and cartographers in a similar way to Wikipedia. OSM data includes manually collected post code data (there was a specific project to collect this), and if your home has been added to the map, it can include comprehensive address data enabling precise geocoding.
There’s that word again - geocoding. OSM providges a service called Nominatim to search OSM data by name and address to give a location. I don’t know, but suspect HASS used Nominatim (or a similar OSM-based service) to turn your address into a location, and show it on a OSM map (look in the bottom right of the window).
The good news is you can improve the data OSM has to find your home. Just as I have been contributing for almost 15 years, and Amazon employees contribute (to help their parcel delivery services), anyone can add their home address to the map.
Basically, you create a point which represents your home, and add tags containing your full address (house number and post code), which can them be used by OSM and HASS to pinpoint your location. As a side effect of open data, many services and businesses (Amazon!) will also be able to find the address.
addr:housenumber = 123
addr:street = Example Street
addr:city = MyTown
addr:postcode = AA99 9AA
addr:country = GB
https://learnosm.org/en/beginner/
Happy Mapping,
James
HASS user, OSM volunteer surveyor and cartographer, Technologist.
If this helps,
this post!