I can't speak to comments rules specifically but I am a heavy user of "agentic" coding and use rules files and while they help they are simply not that reliable. For something like comments that's probably not that big of a deal because some extra bad comments isn't the end of the world.

But I have rules that are quite important for successfully completing a task by my standards and it's very frustrating when the LLM randomly ignores them. In a previous comment I explained my experiences in more detail but depending on the circumstances instruction compliance is 9/10 times at best, with some instructions/tasks as poor as 6/10 in the most "demanding" scenarios particularly as the context window fills up during a longer agentic run.