Problems with Export to SPM8/SPM12

Hello!
When I executed this step"Export to SPM8/SPM12" in the software, I encountered some problems.


In this picture, the Volume downsample factor is set to 5, the size of the Cube obtained is one-fifth of the size of the Cube obtained by setting the Volume downsample factor to 1. And the amplitude of Cube has also changed. The tutorial only mentions that the Volume downsample factor is to limit the size of the files we generate at this step.
But I want to know how to keep and choose the amplitude while reducing the Cube volume in this step? Or in other words, how did the volume of the Cube become 1/5 of its current size?

Looking forward to your reply, thank you.

This option "Volume downsample factor" is documented in the corresponding tutorial:
https://neuroimage.usc.edu/brainstorm/ExportSpm8?highlight=(Volume+downsample)

Set it to 5, you only have one voxel every five in the output volume, in each direction.