Make open file 'finder' larger by default
Generally speaking a window remembers the last size it was set to before closing it. That can and will be overridden on an individual folder basis. EG a folder will usually remember the size and position of the finder window that was opened to view it.
Unfortunately the days of a truly spatial Finder went away with macOS X. So the Mac does not always remember the window size, icon arrangement and such. A feature I really miss from the Classic MacOS days.
But, again, macOS should remember the size that the last Finder window that was opened.