There is a discussion going on in the Bulgarian forum. One of the suggestions was to both include from_level and to_level parameters. Another one was to make all parameters (type, tier, class,...) parallel and on change of any value to refilter all items on auction, but with preserving the values given to parameters from the last filtering (instead of the current tree-like hierarchy, which "forgets" that you were watching for legendary tier 3 items when you switch from one-handed swords to pikes and you have to set the values of category and class again) . Luckily, comrade electroto said they were going to take that into account.