If you are making a new prototype it is always better to start with an existing one and modify. I would base a new A4 prototype on an existing A4 prototype and so forth.
Each prototype file will have a block hypersteelpageframe. This will be a different sized block in each prototype for different sized layouts.
On the standard prototypes I found that the drawings would regularly overlap the edge of the layout. If you pull the frame in from the edge a little then the drawings will fit easier. Shown in screenshot below.