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Thats not right... The lens which goes 1:1 on full frame will go 1:1 (same magnification ratio) on APS-xx format. APS-C cameras are nothing but the smaller sensor cameras compare to full frame... hence your capture area decreases, not the magnification.
You're right, and I didn't put that very well. It's an illusion of creating greater magnification in relation to the lens on all FF sensor via crop. But yes, with a 1:1 lens at MFD focused on a subject 36mm in length, only 23.6mm of the subject will be captured in the frame on an APS-C, which is still 1:1.