You can change the size of time signatures in each layout independently, including changing their vertical position. For example, you can show large time signatures centered on each bracket in full score layouts but standard-sized time signatures on each staff in part layouts.
Procedure
Press Ctrl/Cmd-Shift-L to open Layout Options.
In the Layouts list, select the layouts in which you want to change the size of time signatures.
By default, the layout currently open in the music area is selected when you open the dialog. You can select other layouts by using the selection options in the action bar, clicking and dragging across multiple layouts, Shift-clicking adjacent layouts, and Ctrl/Cmd-clicking individual layouts.
In the category list, click Time Signatures.
Choose one of the following options for Time signature position and size:
Show on every staff
Show once per bracket
Show above the staff
If you chose Show once per bracket, choose one of the following options for Large time signature behavior:
To show a single time signature on each bracketed group, choose Automatic.
To customize the position and vertical alignment of time signatures, choose Manual.
The Manual placement section appears, which contains a table of the bracketed groups with large time signatures in the layout and a list of players not currently set to show large time signatures.
If you chose Manual, do any of the following:
To delete the time signature from a bracketed group, select the bracketed group in the Time Signatures column, then click Remove Large Time Signature Group in the action bar. The players previously in the bracketed group are moved to the Players list.
To define a new bracketed group on which you want to show time signatures, select the corresponding players in the Players list, then click Create Large Time Signature Group in the action bar. The selected players are removed from the Players list.
To change the vertical alignment of time signatures on each bracketed group, double-click in the Vertical alignment field for the corresponding row, then select a vertical alignment from the menu.
Click Apply, then Close.
Result
The size and position of time signatures in the selected layouts is changed.
Showing large time signatures above the staff at system-attached item positions means they do not occupy any rhythmic or horizontal space, whereas the other options do cause time signatures to occupy horizontal space.