In the tab list, notice that, for example, the Download tab has excess space and it doesn't shrink even with the "Reduce tab sizes to fit available space" option enabled.
Furthermore, if the tab list is full (as is the case with the list below), the maximum tab size is not respected because "Reduce tab sizes to fit available space" is enabled.
I don't think that option does what you think it does. 
From the manual:
Reduce tab sizes to fit available space: As the number of tabs increases the size of each tab will be reduced to avoid the tabs overflowing the available space.
It makes the tabs smaller if they won't all fit in the window. It doesn't do anything else.
Your screenshot shows the tabs all fit, so the option is working as it should.
Now I understand. Is there a setting to do what I described?
1- Tab size based on the folder name size (respecting the maximum size) to avoid leaving empty spaces.
Turn off Same size tabs.
Thanks!
