GCA bivariate problem with normalisation of y to x maps

Dear Chao-Gan et al.,

Greetings.
I am running voxelwise bivariate GCA from the GUI. Unfortunately only the x to y maps are getting z transformed, not the y to x maps. Can you suggest a solution? I have a load of y to x maps that I want to normalise using the mean within the mask.

Thank you
Lena