Question re raw image size

When I open a XE1 raw file in SilkyPix the image size is

3264 x 4896

but when I open the same file in ACR the size is

2760 x 4896

Can someone advise me what, if any, preference I have set inadvertently that would explain why ACR doesn't recognize the appropriate raw file size?

Any help or explanation greatly appreciated.

Thanks