image sizing drop down gives incorrect measurements. CC6

For no apparent reason my image sizing drop down is giving me incorrect measurements. A 7360 x 4912 pixel image gives a 24.53 x 16.37 mm Document Size and 3000 resolution. I can enter my desired image size (160 mm on the long side) in the box and change res. to 300 and I will get a print this size on the Epson 3880, but way off-centre (see image below). However the same image will print centred on the Brother office printer. I feel the off-centre problem has something to do with the image sizing issue.  I'm hoping someone might be able to help me on this.  Cheers, Peter