MMR and LP gain/loss in TFT

Can someone explain to me why the hell I lose 25 LP for getting 5h and ~40 for getting 7th while only gaining ~20 LP for getting second? This is pretty stupid and way too punishing. I had some bad games recently but I cannot possibly understand why that should affect my MMR that badly. Especially since I already quite a lot of games. That really stuff really kills my motivation to play if one bad game ruins 3 good games.
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