Better than 1:1
I will take this opportunity to remind us that the infamous "1:1" image magnification, often used as the criterion of "real macro performance" for a lens, is not very definitive with regard to our actual photographic needs.
Almost always, what we are really interested in is what sized object (or object field) will fill our frame. At the "1:1" benchmark, that is a field whose size equals the fame size. For a camera with a four-thirds sensor, that would be an object less than 13.5 mm in diameter (about 2/3 the diameter of an American dime coin).
For an 8" × 10" format camera, that object might be a ladies' shoe.
Ehemm Doug, sorry, but at 1:1 the object size is identical to the size on the sensor, i.e. a 1mm object will be exactly 1mm on the sensor.. . .
It has nothing to do with sensor size nor field size . . .
. . .it is a parameter of the lens only.