Angular orientation of a simple rectangular solid  

Angular orientation of a simple rectangular solid

I'm printing lots of smaller rectangular open-faced boxes as part of an organizer project. One of the boxes I need to print is quite long and narrow (say 220mm x 40mm x 40mm). This is long enough that I am printing the box rotated at 45 degrees so that it can fit on the build plate.

Usually, when I print a box I print it square to the build plate. The first-layer is made up of diagnal lines that touch the outer perimeter at 45 degrees (instead of simply being parallel to the outside of the box). Is this 45 degree rotation of the base layer relative to the walls intentional?

I was surprised to find that when I printed my long box rotated, the base layer lines did not rotate with the model.... rather, the base layer is now square to the outer walls of the print. Setup this way, THE PRINT FAILED ON THE FIRST LAYER. In one of the corners, it seems that the base layer didn't fuse with the outerwall, things quickly curled up, and that was that.

I've discovered that in Prusa Slicer, I can change the Advanced Fill Angle on the Infill Tab from 45 degrees to 0 degrees, and will then get the diagnal pattern I'm used to seeing when printing at the usual orientations.

My question is this. Why the default of having the fill angle be at 45 degrees? Is it possible that the rotation without correcting the Infill orientation was indeed the culprit that failed my last print? Other advice or tips in this vein, or pointers to resources to learn more?

Thanks in advance!