How does the SBMM work? is it based solely on KD, or based on your final position per game, or an amalgamation of different stats? I notice in BR solo's that I usually do pretty poorly in the game directly following a 1st place finish
As far as I'm aware its a whole host of things. Performance to date, total time played, score per minute, average K/D ratio, wins and most recent performance
It will seek out a server will similar skilled players with a low ping first (vs. the person hosting in the party). If it can't find one it will prioritise speed of match making into a low ping server over SBMM.
That's why you get players with 5+ KD in servers with brand new players some times. It's more likely if people in your party are from varying geographic locations. You can play in American servers by having your party leader be someone that lives there.
I created a new account to play with my friends because normally all they do is moan that people are "sweaty" and they average 0.3KD or less (usually ~0.9). The difference is night and day in the lower skill lobbies. I have no useful loadouts on this account, but at least we get to have fun running around instead of being aggressively hunted by people wishing they were Nick Mercs.