What appears to be going on here is the bang is redirecting to /search?q=best+sushi+LA&qa=true, but the following snap ignores any query params when it redirects that to /search?q=best+sushi+LA+site:reddit.com. We'll look into the best way to handle this (which may be passing query params from the current URL when appropriate).
For now, doing @r best sushi LA? may work for giving you what you're looking for.
