get the straps with the "D" style hook on the bottom so they don't come off.
I go from my bars to the center bar and that's it. I made the trip from Holland mi to south of stl many times without issue. I have even hauled a couple rockets that way too, just as far. I also use ratchet straps as I don't trust the pull type.
been using the pull kind for many many years and i have never had one slip. the cheap ones will have the thumb release part bend in making it nearly impossible to use anymore. have had that happen a lot.
i use to not give any fucks about using the metal on my bars until i read an article about how the scratches can cause rust which then make your bars bend easier. sop i started using straps. recently i got these...
love it.
looks to me that you are using the rack wrong. I have one without the wide tie down points at the front as well. The points below the pegs with holes in them are for tying down the foot pegs. This style does not use handle bar tie points. You can use tie downs or short pieces of chain to hook to the foot pegs. I use carabiners on a tie down on both ends. No need for bar tie downs. I tie the rear wheel to the rail.