Season 7 ranked placements

So I'm not here to bitch and whine about where I got places I just am a bit confused on one thing. I was gold 3 last season went 7-3 in solo/duo and got silver 2 seems reasonable to me. However what is strange is I went 5/5 in flex queue and had played in preseason just to make it to gold 5 0 lp and I got placed into silver 1. So what would the reasoning to this be? I mean in flex queue preseason I had few games and a very high win rate so did that cause me to have an overinflated mmr over what I had in solo/duo? Or is it due to there being less of a high spot in the ladder since not many people grinded that much during preseason just to be reset again in flex.