Just tried this with my Hasbro Swindle. I do agree it is too perfect to be accidental, so I can only guess the whole rocket booster concept is the intention, doubling as additional cover for where the head stores rather out-in-the-open in the vehicle back.

While fiddling with my figure and looking stuff up on the wiki, I discovered my Swindle is a post-running retool version with the Hound modification, allowing his gun to connect into his back kibble to be over his shoulder. The slots are present on both sides but for some reason it just doesn't want to work on his right side (the side with the shoulder badge), and the gun detail slightly collides with his head when lowered all the way, but the slots become hinges when attached so I leave mine slightly tilted up, disguising the unpainted gray peg as vaguely internal hydraulics or something.

 

Yeah! That ability to put his gun there in the backpack is really cool. I learned about it from Vangelus' review, and was glad to find that mine had that ability.