Many years ago I was told that unsprung weight is the only part to tie down. The reason it even came up was someone ran a strap over the handle bars on his dirt bike which finished off his front forks.
Back before I knew any better I hauled my Honda Magna in the back of my truck with a single strap from the front corner of the bed, over the triple tree, to the other front corner. Thought nothing of it. 70 miles into my trip on a back, twisty county highway I hit a dip in the middle of a sweeping corner. The bike bounced down becoming free from the single strap, and the momentum tossed the bike into the side of the bed. Dented the shit out of my tank and IIRC the handlebars. The top rail of the bed also sustained some damage. After that, any bike I hauled was two straps tied around the triple tree, and two on the rear rim. A 4x4 placed underneath the frame gave me a solid platform and allowed the springs within the forks to not be fully collapsed.