Detective Partners - Do scenes always get progessively harder?

I'm partnered up in 3 rooms and have contributed enough spins and have enough spin tokens left to ensure my contribution level is around 50% in all three rooms. (I don't want to be a "slacker")

I've played around 11 scenes so far to earn spin tokens, What happens as I progress beyond 11 scenes? Do they still get harder or do they level out. What I don't want to do is partner up in room 4 if I'm approaching or have already reached the limit of my playing ability. That would not be fair to the partner. So what can I expect in scene difficulty after approx 11 scenes? TIA