Ok, had to recheck ALL the postings on this thread just to see what I may have missed...
When doing so I noticed a comment on idle speed problems with the air conditioner on and the note that IAC might need cleaning. how's that been working overall?
FYI, so you don't feel insulted, we see a LOT of non-problems with this type of issue due to manner of figuring mileage or type of use - so we have to start with the "stupid questions" first just to make sure we aren't chasing our tails here while trying to help...
Actual history of mpg over time can be diagnostic of developing problems, in this case it really doesn't seem to be available...
With the age of the car, and the service items you've needed to replace already, I'm wondering what the total mileage is on the car and whether the timing belt has been replaced yet?
It MIGHT be time to "start with the basics", and check the mechanical condition of the engine with a compression check, then check the cam timing/replace the belt if that hasn't been done yet.
The real underlying question here is whether the mpg has been going down over time, or whether this is a sudden change in the "norm" for this car.
The 23 to 25 highway # from before you got it is already a bit low, so there may have been some issues at that time that you still haven't found & addressed.
From what you mentioned in your last post, possibly the easiest first diagnostic would be to drive the car yourself for a bit as you have the Miata, keeping track of actual miles & gallons at each fill to get a good set of mpg numbers for reference.
keep in touch here, and the members will keep throwing out Ideas as you go through the research process to find any issues with the car.
The best function of the forum is to throw out possibilities you can check when you're already out of ideas yourself. It's the thing I miss most working by myself instead of in a shop with other mechanics. The only substitute available is to talk with other friends that work on their vehicles, or for the Focus ask questions here...