Essentially, your LP/League chases your MMR. If your MMR is higher than expected for your current League/Division, you gain substantially more than you lose. On my smurf that has low Plat MMR, I gain 30 per win and lose about 7 per loss in Gold 5. One of my buddies who's in silver loses and gains the same as the OP with a substantially below 50% win rate.
Devi Freak Mint's description below is pretty accurate, though I had a chuckle at tin and wood.
As for dodging, from the League wikia: "Dodging queues may also, to a smaller degree, affect the difference between your MMR and LP (-3LP per first dodge of the day, -10 thereafter)." link