Welcome to Flyertalk, jetset1234. It's good to have you here.

My understanding is that the avios discount option isn't offered when partner flights are involved unless they are on BA codeshares. Since there's no codeshare with HX, you won't get the discount.

Incidentally I wasn't aware that BA offered HX connections on this route. For BAEC members it's better to connect with CX/KA (if prices are the same) as you then earn avios/TPs.