Leauge system

I have managed to rank up for the 4th or 5th time this season and first when I managed to rank out of B5 to B4 nothing changed with my LP gain. 2nd tim I started getting between 17 and 18 for each game and loosing like 19 for eaach lost match. Now I am getting between 12-13 LP for each game and loosing 25+ for each loss. What is the reason for this is happening? And not sure if this is the right bord to put this on but only one I found that makes sence.
Report as:
Offensive Spam Harassment Incorrect Board