I believe the ratios change depending on how many games you win or lose (more you play the less LP you win or lose once you're in the 'right' elo - as determined by your wins/losses)
That is, whenever I first start playing ranked I'll get 30LP for winning and lose 15LP for losing (or something similar)...
but if I'm going 1 for 1 all the time I think league decides I'm at the elo that I'm meant to be at I'm at so I'll gain and lose the same amount (say 15LP) when I win or lose.
Same goes for if I'm losing more often than winning - league decides I'm at an elo that's too high so I'll lose more points when I lose and get more points when I win (ie -30LP for losing and +15 for winning)
That is how it seems to work at least - as far as I've been able to determine.