There is no such thing as a "macro" if its below 1:1 Shame on Zeiss.
1:1 ratio is a subjective value. You get more magnification with 1:1 macro on crop, than with 1:1 macro on FF.
Something like A7R (36mp sensor) allows you to crop a lot and get the same magnification of a 16mp crop sensor. So, technically, 1:2 macro on 20mp crop provides similar magnification to 1:1 macro on 12mp FF.
1:1 has nothing to do with megapixels; it is entirely governed by optics and means the physical size of the projected image equals that of the subject, ie a 1cm tall object results in a 1cm tall projected image.
Due to the cropping factor of an aps-c sensor though, you are effectively blowing up the projected image. So this means that for a crop factor of 1.5, a 50 mm lens will become 75 mm equivalent, and at 1:2 magnification becomes 3/4 magnification.
5D3, 5D2, Sony α6000, G16 | SY14 f/2.8, 24 f/2.8, 35 f/2, Ʃ35 f/1.4A, 50 f/1.8 I, Ʃ50 f/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200 f/2.8L IS II, 1.4x II, 2.0x III, 70-300L | E-mount: SY12 f/2, 35 F1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY 300 F6.3 ED UMC CS, MB Speed Booster and Canon FD(n) & FL lenses