I hear ya. Difference between 32-33 and 27 mpg isn't all that much. But on the other hand, if you're still getting 27 mpg in the city, then maybe your city driving isn't all that hard core, so maybe it doesn't call for shortening the OCI that much. Now, if you were in some really bad back-to-back traffic with lots of idling, I'm sure your MPG would be significantly worse.Point taken but as an example my CX5 gets 32-33mpg on the highway. That could drop to 27 in city for example but the result would still be a long OCI in my view. Now that is a personal opinion on my part and not scientific in any way.
It is a good point though.
Google Docs BITOG OCI Calculator link