I bought a tune for my ND Miata shortly after I got the car.
https://bbrgti.com/blogs/news/bbr-un...-mx-5-miata-nd
They have a dyno plot showing +21hp and +15ft-lbs, from a 1.5L, bringing it up to ~160hp. This engine has a 14.0:1 compression ratio and runs Atkinson cycle. They also advertise a fuel economy improvement. When I spoke with the tuner personally, I asked how it would impact fuel economy, and he said "not at all".
My guess is that additional power is made by running a bit less valve overlap (Atkinson cycle) and a bit less ignition timing to make up for thee extra air being let into the cylinder. If that's the case, I'd imagine it would be an economy loss under WOT - the two are mutually exclusive in this kind of engine. If they simply tweaked the ignition table, it would be a (minor) fuel economy gain.
Unfortunately, the tune is locked, and I can't see what they've actually done to it. I can only flash it, or flash back to stock.