The thing is, making a zone system placement of important tones in the scene IS the only reliable (aka "precise") way to meter transparency film. You don't really want an accurate metering methodology, you want precise metering methodology, because then that's easy to adjust to give you bang-on results.

If you can spot meter individual parts of a scene and you know what the latitude of the film is, then averaging isn't doing anything for you - you already know all you need to come up with the right exposure every time, short of human error or lapses in judgement.

Basically, someone should be able to ask you where you would place various typical elements of the sorts of scenes you shoot in terms of zones/EVs, and you should be able to tell them - because you need to answer that same question to yourself every time you pick up the meter. If you can't answer it, then this is your problem. The solution to that is just a bit of decision making based on past (and possibly future) results. That's the critical step.

If you're already making those decisions and you're consistently under or over exposing then that's easy enough to correct too.