Is it possible to pass in variables for x,y,z location in atxd3?

I'm using the reactive pellet bed and making a lot of use of atxd2 and atxd3 functions to plot concentrations inside the particles. The format is atxd3(x,y,z,variable). Instead of specifying x,y and z, I would like to pass in variables. This would allow me to look at te same relative positions in my catalyst beds irrespective of size and shape of bed.