Hello Hernán Galeano,
Thanks for reaching out to the Tableau Community. For questions like this I find it is very helpful to attach a workbook so the Tableau Community can get some hands on investigation done. Please review the link below for adding workbooks to a post.
I was able to build a small example viz and the marks maintained a consistent size when used on two different worksheets. I am attaching my example. Feel free to mock up something using this workbook that demonstrates the behavior that you are encountering.
Hope this helps!
Matching Size Example.twbx 369.9 KB