Riot's algorithm (as is any for any major game) is proprietary and a trade secret. You're not going to get details.
You cannot take win/loss streaks as a means to determine your MMR, nor can you use your rank to determine MMR. MMR is completely separate from rank.
First of all, I'm far from being the only one who's noticed this, as the League boards are littered with other people who've brought up the same issue and how they've noticed it affecting them. Regardless of this being a "trade secret," you should be matching people up of equal skill and rank - not a gold 4 with a bunch of people hovering around silver 3. What's the point of a ranking system if I'm not playing with people of equal skill and rank, or even of the same division? Why is it that for ten games I'll be put in matches with people with a good recent match history and then all of a sudden after having gained a substantial amount of LP, I - AND MANY OTHERS - are then placed into consecutive matches with people with terrible match histories of majority losses/feeds/AFKs; why should people who are on winning streaks then be matched up all of a sudden - and consistently - with people who are on losing streaks, almost guaranteeing failure for the individual on a win streak? I'm sure that you guys are doing this, just as numerous other games like Overwatch do as well, just to push a 50% win/loss ratio. As I've said, I'm far from being the only one who's noticed or been affected by this.
Are you denying that your algorithm is designed to try as hard as it can to ensure that the majority of people end up hovering around a 50% ratio? An algorithm that is commonly used in other arena/moba games is not a secret when countless others can blatantly see what's going on.