Doesn't that get too wide with a wheel on each side of the frame?
Width can be an issue. When packing a bike like the PX10, I seek a box with a width of at least 8". This usually allows me to fit everything in, snugly. And, more often than not, once fitted into the box, the alxe protectors, on the axle ends, are actually always in contact with the sides of the box.
The "box" had been cut down so severely and carefully that it fit the frame/fork like a glove - tailored, it was.
Tailored? I like that word and that is the best one to use, when describing what one needs to do to a box and the bike.
Take you time in fitting the box and bike. And it does take time. I never rush a packing job and I frequently pack and repack, until I am satisfied that I can do no better, with what I have.