@Godisbullen don't know the details and I am not sure if there is an official info how SBMM should be working and in which mode or what parameters it take into account...
As I said my experience with "public" type of games has always been and remain one = it is free for all = place where people go make crazy youtube frag movies, try now things, new moves, explore the maps, do stupid stuff. Most of the players always have been cannonball meat in every game I played before.
Also I am not sure if to be honest same settings of SBMM should be applied to pulic and ranked. Imagine if a Predator or Master player just wants to explore the map or warm up...they would have to wait those crazy long loading times as they do in ranked just to get to the game equivalent to ranked and fail to warm up / explore the map as everyone would again tend to play it as ranked at that level or instantly destroy people who came to "just have fun"...
In any case more info on SBMM from Respawn would clarify things but I guess that's not their style, they rather cash in while making us guess and keep the forum active with posts like this (probably sold some google ads as well).