What you’re describing is perfectly normal. My dream signs tend to be pretty ordinary as well: being in school (as both a student and as my real-life job as a teacher), bathrooms, and my old house/neighborhood, so don’t think you’re the only one.
RCing only to dream signs does make it difficult to catch all cases, because that’s only part of it. The other half of RCing is making a habit of asking yourself throughout the day if you’re dreaming and reality checking in response to the question (as opposed to making a habit of just RCing without questioning). This will help you with the normal situations, meaning that when you find a strange dream situation to be normal, you still have a chance to RC. Work with these two different reality check triggers instead of one and you’ll certainly see your lucidity rate go up.