If the manual states it will take a 27" plate in the lowest position and it does, it would be good will on their part, but honestly, after 6 weeks, that feels like you didn't prioritize it.
If the manual states it will take a 27" plate in the lowest position and it doesn't, then you are entitled to a refund. Clearly not fit for purpose.
If the manual states it will take a 27" AND glasses in the same load whilst that tray is in the lowest position and doesn't same as above, but if it makes no assertions (and I suspect it won't), then the first thing applies.

