you have the 'Safety Stance' suspension, which means the axles are spread apart. I have the same thing. I don't know the distance between them, but I do know that the conventional X-chocks will not work.
I cannot tell by the picture what type you purchased.
I got some that were designed for wide stance axles, and they work well, although a bit awkward to install.
Personally, I think a couple of scissor jacks to the ground at mid-point would work better for stability. I experimented a little bit with that, and concluded that it is more stable than X-chocks for the wide stance units.
I hope that helps.
Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4