How does Ranked 5s Matchmaking Work?

I'm curious if anyone knows why the system seems to continually match our 5s team well above our current rank.

My friends and I have a Gold IV 5s team and are consistently matched against Platinum+ 5s teams. Our soloqueue ranks are predominantly low Platinum with a Gold player and a Silver player. The soloqueue ranks of those we are matched up against are typically mid Diamond with the odd Platinum or Master tier player.

This isn't complaining so much as a genuine curiosity. Why pit a Gold IV team against teams that are over a whole league ahead of us? I have a hard time believing our team MMR is that much above our current position. Does anything else factor in?