BoostMatch not working for category

Hi!

So we have a recipe search page where an editor can choose e.g. christmas as the active category, and then we want all the recipes that are tagged with the category christmas to show up first.

I tried this: 

var searchResult = findClient.Search<RecipePage>(Language.Norwegian).BoostMatching(x => x.TypeCategory.Match(activeCategory.ToString()), 1).GetContentResult();

But it doesn't seem to work. It gives the exact same result as if I don't boost. If I filter on the same category, I get the recipes I want:

var searchResult = findClient.Search<RecipePage>(Language.Norwegian).Filter(x => x.TypeCategory.Match(activeCategory.ToString())).GetContentResult();

What am I doing wrong? Is there a better way to solve this?