Matching higher ranking players

I was ranked gold 5 even though im a platinum player and had good placement games but that would be fine unless I would still be matchmaking diamonds and low onyxes after being ranked. Its insanely annoying because when I lose my rank lessens by the same amount it would when I was high platinum.
What can I do about this?

Hey OP. The Matchmaking Feedback topics that are pinned in the Matchmaking forums are the best place to post the links you provided above. They give in-depth explanations of the ranking system and if you still have any questions feel free to make a post in the latest pinned thread with the information your provided and any questions you have