Global calibration or not in the use of isosurface in bonej

Dear Imagej’s users and developers,
I’m Daniela. At the moment I’m working on x ray micro tomographyc images of open cells Al foams.
I’m using Bonej to calculate the relative density (BV/TV) and the internal surface area (BS) of the samples.
When applying “isosurface” I realized that the program gives different surface values depending if the global calibration is setted or not.
To have an idea of the differences involved I bilt a known 3D image.
Tht is, I bilt a central white cube, that I consider as the solid contribution, surrounded by 6 black cubes, considered as empty sapces.

I calibrated the image whith pixel size of 0.02 mm.
I thresholded the image using Otsu method. I used different values of resampling when using “isosurface”.
I obtained the following results:

without global calibration

with global calibration

Do you have any advice? Do I have to use or not the global calibration?

Thank you in andance