Usually, the first page has a smaller space for the frame than the frames in the other pages due to the area for the title and composer of the piece as well as additional information.
Dorico has lots of empty space under the system if there is only one system. Otherwise, the space between the two staves is too large.
The size of the system or the size of each staff must be resized to control this problem.
How could I do this in Dorico?
Making the bars in a frame after selecting the systems which should appear in the first page makes the systems collide as the attachment:
I have a further related question about it.
I have found the font size option in the “Edit Font Styles” window.
As far as I understand, “Staff-relative” size of the font is the best option for changing staff size on specific pages.
However, I see some font styles of which the font size is not activated as follows:
Should I turn on or not? Should I turn on it and set it to “Staff-relative” size.
Do I think correctly? Why is the default value deactivated?
You don’t need to change this setting: when it is disabled like that, it’s showing that it is inheriting that value from its parent font style.