Yeah, in general, the more converged your image will be, the less detail will you lose (denoiser radius has significant impact on it too). You can get clean image with denoiser even after 10 passes, but do not expect detail to remain there. You will need to reach at the very least 10% noise limit to have enough information to denoise. As Ondra said, it's not a magic wand and won't give you clean detailed image out of undercooked renders.