Isn‘t this a part of the problem? The urea tanks are way too small and need refilling way too seldom which means a too low urea usage? Volkswagen wanted urea to be refilled by your service station and not by the customers themselves because they might have found this inconvenient.
[1] https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=16677&...
[2] https://www.govinfo.gov/content/pkg/FR-2009-11-09/pdf/E9-269...
[3] https://www.govinfo.gov/content/pkg/FR-2014-08-08/pdf/2014-1...
I know VW managers first thought Urea was an inconvenience to have at all, then an inconvenience for owners to refill so should last a service interval. My new car has a Urea tank and isn’t a diesel-gate car. It need to refill maybe 1 time before the service intervals. I can’t see why it would be considered inconvenient - it’s easier to refill than windshield wiper fluid (that you need to pop the hood for!). So if it would have come at a price of 20L diesel capacity space, and require refills every month, I still wouldn’t have found it inconvenient.
I don’t know how they determine how much AdBlue to consume now, but I’m guessing since they now manage to comply with regulation they just use as little as possible? If they can further limit emissions by using more, then there’s some headroom for improving too.
Depending on the engine, driving style, etc, it should really be using something on the order of 20-60 litres of AdBlue per 1000 litres of diesel.