1 - the position of the layer break itself.
2 - the transcode status of the video files, and
3 - the amount of content on the disc.
Both (2) and (3) will affect (1), and you could even add a subset of (3) stating the "sequence or order timelines were added to the project".
Are you saying the order I build my project can determine if a layer break will work? Should I place my long 2 hour movie in the project first and then place all my bonus video and then place all my menus?
My movie timeline takes up 4.3 GBs of space The remaining files take an additional 4 GBs of space